feat(adapter): add BigDecimal kotlin support (#8880)

* feat(adapter): add BigDecimal kotlin support

this allows the kotlin client generator to support
BigDecimal values

Fixes #7196

* update samples

Co-authored-by: William Cheng <wing328hk@gmail.com>

samples/client/petstore/kotlin-json-request-string/src/main/kotlin/org/openapitools/client/infrastructure/BigDecimalAdapter.kt

@@ -0,0 +1,17 @@
+package org.openapitools.client.infrastructure
+
+import com.squareup.moshi.FromJson
+import com.squareup.moshi.ToJson
+import java.math.BigDecimal
+
+class BigDecimalAdapter {
+    @ToJson
+    fun toJson(value: BigDecimal): String {
+        return value.toPlainString()
+    }
+
+    @FromJson
+    fun fromJson(value: String): BigDecimal {
+        return BigDecimal(value)
+    }
+}

samples/client/petstore/kotlin-json-request-string/src/main/kotlin/org/openapitools/client/infrastructure/BigIntegerAdapter.kt

@@ -0,0 +1,17 @@
+package org.openapitools.client.infrastructure
+
+import com.squareup.moshi.FromJson
+import com.squareup.moshi.ToJson
+import java.math.BigInteger
+
+class BigIntegerAdapter {
+    @ToJson
+    fun toJson(value: BigInteger): String {
+        return value.toString()
+    }
+
+    @FromJson
+    fun fromJson(value: String): BigInteger {
+        return BigInteger(value)
+    }
+}

samples/client/petstore/kotlin-json-request-string/src/main/kotlin/org/openapitools/client/infrastructure/Serializer.kt

@@ -13,6 +13,8 @@ object Serializer {
         .add(UUIDAdapter())
         .add(ByteArrayAdapter())
         .add(KotlinJsonAdapterFactory())
+        .add(BigDecimalAdapter())
+        .add(BigIntegerAdapter())
 
     @JvmStatic
     val moshi: Moshi by lazy {