make title available to templates for ref properties (#17881)

Even though `title` is technically for the title of the API itself,
it's possible to set it for properties as well.
Right now, the `title` property is available in templates for regular properties,
but for ref-properties it gets lost right here.
This seemed rather surprising to me, so I think it's better to fix.

modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java

@@ -4235,6 +4235,9 @@ public class DefaultCodegen implements CodegenConfig {
             if (original.getMinimum() != null) {
                 property.setMinimum(String.valueOf(original.getMinimum().doubleValue()));
             }
+            if (original.getTitle() != null) {
+                property.setTitle(original.getTitle());
+            }
         }
 
         // set the default value

modules/openapi-generator/src/test/java/org/openapitools/codegen/DefaultCodegenTest.java

@@ -1916,6 +1916,19 @@ public class DefaultCodegenTest {
         Assert.assertFalse(codegen.fromProperty("customerCode", (Schema) requestProperties.get("customerCode")).deprecated);
     }
 
+    @Test
+    public void testTitleProperty() {
+        final OpenAPI openAPI = TestUtils.parseFlattenSpec("src/test/resources/3_0/property-title.yaml");
+        new InlineModelResolver().flatten(openAPI);
+        final DefaultCodegen codegen = new DefaultCodegen();
+        codegen.setOpenAPI(openAPI);
+
+        final Map testProperties = Collections.unmodifiableMap(openAPI.getComponents().getSchemas().get("ModelWithTitledProperties").getProperties());
+
+        Assert.assertEquals("Simple-Property-Title", codegen.fromProperty("simpleProperty", (Schema) testProperties.get("simpleProperty")).title);
+        Assert.assertEquals("Ref-Property-Title", codegen.fromProperty("refProperty", (Schema) testProperties.get("refProperty")).title);
+    }
+
     @Test
     public void testDeprecatedRef() {
         final OpenAPI openAPI = TestUtils.parseSpec("src/test/resources/3_0/model-deprecated.yaml");

modules/openapi-generator/src/test/resources/3_0/property-title.yaml

@@ -0,0 +1,29 @@
+openapi: 3.0.1
+paths:
+  /foo:
+    get:
+      responses:
+        '200':
+          description: ok
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/test'
+info:
+  title: Title on Properties
+  version: "1.0"
+components:
+  schemas:
+    ModelWithTitledProperties:
+      properties:
+        simpleProperty:
+          type: string
+          title: Simple-Property-Title
+        refProperty:
+          type: string
+          title: Ref-Property-Title
+          allOf:
+            - $ref: '#/components/schemas/RefObject'
+      type: object
+    RefObject:
+      type: string