[java][Okhttp] replace okhttp-gson with okhttp-gson-nextgen (#11538)

* replace okhttp-gson with okhttp-gson-nextgen

* add new files

* update doc

* clean up pom

* update test

* restore error handling in doc

* add back changes

* uncomment tests

* update samples

samples/client/petstore/java/okhttp-gson/.openapi-generator/FILES

@@ -4,37 +4,48 @@ README.md
 api/openapi.yaml
 build.gradle
 build.sbt
-docs/AdditionalPropertiesAnyType.md
-docs/AdditionalPropertiesArray.md
-docs/AdditionalPropertiesBoolean.md
 docs/AdditionalPropertiesClass.md
-docs/AdditionalPropertiesInteger.md
-docs/AdditionalPropertiesNumber.md
-docs/AdditionalPropertiesObject.md
-docs/AdditionalPropertiesString.md
 docs/Animal.md
 docs/AnotherFakeApi.md
+docs/Apple.md
+docs/AppleReq.md
 docs/ArrayOfArrayOfNumberOnly.md
 docs/ArrayOfNumberOnly.md
 docs/ArrayTest.md
-docs/BigCat.md
-docs/BigCatAllOf.md
+docs/Banana.md
+docs/BananaReq.md
+docs/BasquePig.md
 docs/Capitalization.md
 docs/Cat.md
 docs/CatAllOf.md
 docs/Category.md
 docs/ClassModel.md
 docs/Client.md
+docs/ComplexQuadrilateral.md
+docs/DanishPig.md
+docs/DefaultApi.md
+docs/DeprecatedObject.md
 docs/Dog.md
 docs/DogAllOf.md
+docs/Drawing.md
 docs/EnumArrays.md
 docs/EnumClass.md
 docs/EnumTest.md
+docs/EquilateralTriangle.md
 docs/FakeApi.md
 docs/FakeClassnameTags123Api.md
 docs/FileSchemaTestClass.md
+docs/Foo.md
 docs/FormatTest.md
+docs/Fruit.md
+docs/FruitReq.md
+docs/GmFruit.md
+docs/GrandparentAnimal.md
 docs/HasOnlyReadOnly.md
+docs/HealthCheckResult.md
+docs/InlineResponseDefault.md
+docs/IsoscelesTriangle.md
+docs/Mammal.md
 docs/MapTest.md
 docs/MixedPropertiesAndAdditionalPropertiesClass.md
 docs/Model200Response.md
@@ -43,21 +54,38 @@ docs/ModelFile.md
 docs/ModelList.md
 docs/ModelReturn.md
 docs/Name.md
+docs/NullableClass.md
+docs/NullableShape.md
 docs/NumberOnly.md
+docs/ObjectWithDeprecatedFields.md
 docs/Order.md
 docs/OuterComposite.md
 docs/OuterEnum.md
+docs/OuterEnumDefaultValue.md
+docs/OuterEnumInteger.md
+docs/OuterEnumIntegerDefaultValue.md
+docs/ParentPet.md
 docs/Pet.md
 docs/PetApi.md
+docs/PetWithRequiredTags.md
+docs/Pig.md
+docs/Quadrilateral.md
+docs/QuadrilateralInterface.md
 docs/ReadOnlyFirst.md
+docs/ScaleneTriangle.md
+docs/Shape.md
+docs/ShapeInterface.md
+docs/ShapeOrNull.md
+docs/SimpleQuadrilateral.md
 docs/SpecialModelName.md
 docs/StoreApi.md
 docs/Tag.md
-docs/TypeHolderDefault.md
-docs/TypeHolderExample.md
+docs/Triangle.md
+docs/TriangleInterface.md
 docs/User.md
 docs/UserApi.md
-docs/XmlItem.md
+docs/Whale.md
+docs/Zebra.md
 git_push.sh
 gradle.properties
 gradle/wrapper/gradle-wrapper.jar
@@ -81,6 +109,7 @@ src/main/java/org/openapitools/client/ServerConfiguration.java
 src/main/java/org/openapitools/client/ServerVariable.java
 src/main/java/org/openapitools/client/StringUtil.java
 src/main/java/org/openapitools/client/api/AnotherFakeApi.java
+src/main/java/org/openapitools/client/api/DefaultApi.java
 src/main/java/org/openapitools/client/api/FakeApi.java
 src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
 src/main/java/org/openapitools/client/api/PetApi.java
@@ -94,34 +123,45 @@ src/main/java/org/openapitools/client/auth/OAuth.java
 src/main/java/org/openapitools/client/auth/OAuthFlow.java
 src/main/java/org/openapitools/client/auth/OAuthOkHttpClient.java
 src/main/java/org/openapitools/client/auth/RetryingOAuth.java
-src/main/java/org/openapitools/client/model/AdditionalPropertiesAnyType.java
-src/main/java/org/openapitools/client/model/AdditionalPropertiesArray.java
-src/main/java/org/openapitools/client/model/AdditionalPropertiesBoolean.java
+src/main/java/org/openapitools/client/model/AbstractOpenApiSchema.java
 src/main/java/org/openapitools/client/model/AdditionalPropertiesClass.java
-src/main/java/org/openapitools/client/model/AdditionalPropertiesInteger.java
-src/main/java/org/openapitools/client/model/AdditionalPropertiesNumber.java
-src/main/java/org/openapitools/client/model/AdditionalPropertiesObject.java
-src/main/java/org/openapitools/client/model/AdditionalPropertiesString.java
 src/main/java/org/openapitools/client/model/Animal.java
+src/main/java/org/openapitools/client/model/Apple.java
+src/main/java/org/openapitools/client/model/AppleReq.java
 src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
 src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
 src/main/java/org/openapitools/client/model/ArrayTest.java
-src/main/java/org/openapitools/client/model/BigCat.java
-src/main/java/org/openapitools/client/model/BigCatAllOf.java
+src/main/java/org/openapitools/client/model/Banana.java
+src/main/java/org/openapitools/client/model/BananaReq.java
+src/main/java/org/openapitools/client/model/BasquePig.java
 src/main/java/org/openapitools/client/model/Capitalization.java
 src/main/java/org/openapitools/client/model/Cat.java
 src/main/java/org/openapitools/client/model/CatAllOf.java
 src/main/java/org/openapitools/client/model/Category.java
 src/main/java/org/openapitools/client/model/ClassModel.java
 src/main/java/org/openapitools/client/model/Client.java
+src/main/java/org/openapitools/client/model/ComplexQuadrilateral.java
+src/main/java/org/openapitools/client/model/DanishPig.java
+src/main/java/org/openapitools/client/model/DeprecatedObject.java
 src/main/java/org/openapitools/client/model/Dog.java
 src/main/java/org/openapitools/client/model/DogAllOf.java
+src/main/java/org/openapitools/client/model/Drawing.java
 src/main/java/org/openapitools/client/model/EnumArrays.java
 src/main/java/org/openapitools/client/model/EnumClass.java
 src/main/java/org/openapitools/client/model/EnumTest.java
+src/main/java/org/openapitools/client/model/EquilateralTriangle.java
 src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+src/main/java/org/openapitools/client/model/Foo.java
 src/main/java/org/openapitools/client/model/FormatTest.java
+src/main/java/org/openapitools/client/model/Fruit.java
+src/main/java/org/openapitools/client/model/FruitReq.java
+src/main/java/org/openapitools/client/model/GmFruit.java
+src/main/java/org/openapitools/client/model/GrandparentAnimal.java
 src/main/java/org/openapitools/client/model/HasOnlyReadOnly.java
+src/main/java/org/openapitools/client/model/HealthCheckResult.java
+src/main/java/org/openapitools/client/model/InlineResponseDefault.java
+src/main/java/org/openapitools/client/model/IsoscelesTriangle.java
+src/main/java/org/openapitools/client/model/Mammal.java
 src/main/java/org/openapitools/client/model/MapTest.java
 src/main/java/org/openapitools/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
 src/main/java/org/openapitools/client/model/Model200Response.java
@@ -130,15 +170,32 @@ src/main/java/org/openapitools/client/model/ModelFile.java
 src/main/java/org/openapitools/client/model/ModelList.java
 src/main/java/org/openapitools/client/model/ModelReturn.java
 src/main/java/org/openapitools/client/model/Name.java
+src/main/java/org/openapitools/client/model/NullableClass.java
+src/main/java/org/openapitools/client/model/NullableShape.java
 src/main/java/org/openapitools/client/model/NumberOnly.java
+src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
 src/main/java/org/openapitools/client/model/Order.java
 src/main/java/org/openapitools/client/model/OuterComposite.java
 src/main/java/org/openapitools/client/model/OuterEnum.java
+src/main/java/org/openapitools/client/model/OuterEnumDefaultValue.java
+src/main/java/org/openapitools/client/model/OuterEnumInteger.java
+src/main/java/org/openapitools/client/model/OuterEnumIntegerDefaultValue.java
+src/main/java/org/openapitools/client/model/ParentPet.java
 src/main/java/org/openapitools/client/model/Pet.java
+src/main/java/org/openapitools/client/model/PetWithRequiredTags.java
+src/main/java/org/openapitools/client/model/Pig.java
+src/main/java/org/openapitools/client/model/Quadrilateral.java
+src/main/java/org/openapitools/client/model/QuadrilateralInterface.java
 src/main/java/org/openapitools/client/model/ReadOnlyFirst.java
+src/main/java/org/openapitools/client/model/ScaleneTriangle.java
+src/main/java/org/openapitools/client/model/Shape.java
+src/main/java/org/openapitools/client/model/ShapeInterface.java
+src/main/java/org/openapitools/client/model/ShapeOrNull.java
+src/main/java/org/openapitools/client/model/SimpleQuadrilateral.java
 src/main/java/org/openapitools/client/model/SpecialModelName.java
 src/main/java/org/openapitools/client/model/Tag.java
-src/main/java/org/openapitools/client/model/TypeHolderDefault.java
-src/main/java/org/openapitools/client/model/TypeHolderExample.java
+src/main/java/org/openapitools/client/model/Triangle.java
+src/main/java/org/openapitools/client/model/TriangleInterface.java
 src/main/java/org/openapitools/client/model/User.java
-src/main/java/org/openapitools/client/model/XmlItem.java
+src/main/java/org/openapitools/client/model/Whale.java
+src/main/java/org/openapitools/client/model/Zebra.java