[kotlin][client] Some kotlin client enhancements

- Don't use JsonFormat for Date objects, this should be controlled via
  a custom serializer/deserializer or a turning on and off serialization
  features of Jackson.  I've updated the jacksonObjectMapper config to
  write the dates as strings, which I think was intended in the original
  commit.
  https://fasterxml.github.io/jackson-databind/javadoc/2.6/com/fasterxml/jackson/databind/SerializationFeature.html#WRITE_DATES_AS_TIMESTAMPS
  https://fasterxml.github.io/jackson-databind/javadoc/2.6/com/fasterxml/jackson/databind/cfg/MapperConfig.html#getDateFormat--
- Dont' use @jsonformat(shape = JsonFormat.Shape.OBJECT) for enums.
  This causes Enums to be formatted as objects with an internal "value"
  field.  In reality, OpenAPI enums are just strings without properties
  and should be treated as a string.
  https://www.baeldung.com/jackson-serialize-enums#2-enum-as-json-object
- Add's Kotlin use site annotation @get: to JsonProperty for parent interface
  properties.  Otherwise Kotlin will warn:
  "This annotation is not applicable to target 'member property without
  backing field or delegate'"
- Add's JsonTypeInfo annotations to interfaces for inheritance.  This
  was copied verbatim from the kotlin-spring generator.
  https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/kotlin-spring/typeInfoAnnotation.mustache

modules/openapi-generator/src/main/resources/kotlin-client/data_class.mustache

@@ -10,7 +10,10 @@ import com.squareup.moshi.JsonClass
 {{/moshi}}
 {{#jackson}}
 import com.fasterxml.jackson.annotation.JsonProperty
-import com.fasterxml.jackson.annotation.JsonFormat
+{{#discriminator}}
+import com.fasterxml.jackson.annotation.JsonSubTypes
+import com.fasterxml.jackson.annotation.JsonTypeInfo
+{{/discriminator}}
 {{/jackson}}
 {{#parcelizeModels}}
 import android.os.Parcelable
@@ -34,7 +37,7 @@ import java.io.Serializable
 {{#parcelizeModels}}
 @Parcelize
 {{/parcelizeModels}}
-{{#multiplatform}}@Serializable{{/multiplatform}}{{#moshi}}{{#moshiCodeGen}}@JsonClass(generateAdapter = true){{/moshiCodeGen}}{{/moshi}}
+{{#multiplatform}}@Serializable{{/multiplatform}}{{#moshi}}{{#moshiCodeGen}}@JsonClass(generateAdapter = true){{/moshiCodeGen}}{{/moshi}}{{#jackson}}{{#discriminator}}{{>typeInfoAnnotation}}{{/discriminator}}{{/jackson}}
 {{#nonPublicApi}}internal {{/nonPublicApi}}{{#discriminator}}interface{{/discriminator}}{{^discriminator}}data class{{/discriminator}} {{classname}}{{^discriminator}} (
 {{#vars}}
 {{#required}}{{>data_class_req_var}}{{/required}}{{^required}}{{>data_class_opt_var}}{{/required}}{{^-last}},{{/-last}}
@@ -57,7 +60,6 @@ import java.io.Serializable
     * Values: {{#allowableValues}}{{#enumVars}}{{&name}}{{^-last}},{{/-last}}{{/enumVars}}{{/allowableValues}}
     */
     {{#multiplatform}}@Serializable(with = {{nameInCamelCase}}.Serializer::class){{/multiplatform}}
-    {{#jackson}}{{#isPrimitiveType}}@JsonFormat(shape = JsonFormat.Shape.NATURAL){{/isPrimitiveType}}{{^isPrimitiveType}}@JsonFormat(shape = JsonFormat.Shape.OBJECT){{/isPrimitiveType}}{{/jackson}}
     {{#nonPublicApi}}internal {{/nonPublicApi}}enum class {{{nameInCamelCase}}}(val value: {{#isListContainer}}{{{ nestedType }}}{{/isListContainer}}{{^isListContainer}}{{{dataType}}}{{/isListContainer}}){
     {{#allowableValues}}
     {{#enumVars}}

modules/openapi-generator/src/main/resources/kotlin-client/data_class_opt_var.mustache

@@ -9,9 +9,6 @@
     @SerializedName("{{{vendorExtensions.x-base-name-literal}}}")
     {{/gson}}
     {{#jackson}}
-    {{#isDateTime}}
-    @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "dd-MM-yyyy hh:mm:ss")
-    {{/isDateTime}}
     @JsonProperty("{{{vendorExtensions.x-base-name-literal}}}")
     {{/jackson}}
     {{/multiplatform}}

modules/openapi-generator/src/main/resources/kotlin-client/data_class_req_var.mustache

@@ -9,9 +9,6 @@
     @SerializedName("{{{vendorExtensions.x-base-name-literal}}}")
     {{/gson}}
     {{#jackson}}
-    {{#isDateTime}}
-    @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "dd-MM-yyyy hh:mm:ss")
-    {{/isDateTime}}
     @JsonProperty("{{{vendorExtensions.x-base-name-literal}}}")
     {{/jackson}}
     {{/multiplatform}}

modules/openapi-generator/src/main/resources/kotlin-client/enum_class.mustache

@@ -5,6 +5,9 @@ import com.google.gson.annotations.SerializedName
 {{#moshi}}
 import com.squareup.moshi.Json
 {{/moshi}}
+{{#jackson}}
+import com.fasterxml.jackson.annotation.JsonProperty
+{{/jackson}}
 {{/multiplatform}}
 {{#multiplatform}}
 import kotlinx.serialization.*
@@ -16,7 +19,6 @@ import kotlinx.serialization.internal.CommonEnumSerializer
 * Values: {{#allowableValues}}{{#enumVars}}{{&name}}{{^-last}},{{/-last}}{{/enumVars}}{{/allowableValues}}
 */
 {{#multiplatform}}@Serializable(with = {{classname}}.Serializer::class){{/multiplatform}}
-{{#jackson}}@JsonFormat(shape = JsonFormat.Shape.OBJECT){{/jackson}}
 {{#nonPublicApi}}internal {{/nonPublicApi}}enum class {{classname}}(val value: {{{dataType}}}){
 
 {{#allowableValues}}{{#enumVars}}

modules/openapi-generator/src/main/resources/kotlin-client/interface_opt_var.mustache

@@ -9,10 +9,7 @@
     @SerializedName("{{{vendorExtensions.x-base-name-literal}}}")
     {{/gson}}
     {{#jackson}}
-    {{#isDateTime}}
-    @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "dd-MM-yyyy hh:mm:ss")
-    {{/isDateTime}}
-    @JsonProperty("{{{vendorExtensions.x-base-name-literal}}}")
+    @get:JsonProperty("{{{vendorExtensions.x-base-name-literal}}}")
     {{/jackson}}
     {{/multiplatform}}
     {{#multiplatform}}@SerialName(value = "{{{vendorExtensions.x-base-name-literal}}}") {{/multiplatform}}{{>modelMutable}} {{{name}}}: {{#isEnum}}{{#isListContainer}}{{#isList}}kotlin.collections.List{{/isList}}{{^isList}}kotlin.Array{{/isList}}<{{classname}}.{{{nameInCamelCase}}}>{{/isListContainer}}{{^isListContainer}}{{classname}}.{{{nameInCamelCase}}}{{/isListContainer}}{{/isEnum}}{{^isEnum}}{{{dataType}}}{{/isEnum}}?

modules/openapi-generator/src/main/resources/kotlin-client/interface_req_var.mustache

@@ -9,10 +9,7 @@
     @SerializedName("{{{vendorExtensions.x-base-name-literal}}}")
     {{/gson}}
     {{#jackson}}
-    {{#isDateTime}}
-    @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "dd-MM-yyyy hh:mm:ss")
-    {{/isDateTime}}
-    @JsonProperty("{{{vendorExtensions.x-base-name-literal}}}")
+    @get:JsonProperty("{{{vendorExtensions.x-base-name-literal}}}")
     {{/jackson}}
     {{/multiplatform}}
     {{#multiplatform}}@SerialName(value = "{{{vendorExtensions.x-base-name-literal}}}") @Required {{/multiplatform}}{{>modelMutable}} {{{name}}}: {{#isEnum}}{{#isListContainer}}{{#isList}}kotlin.collections.List{{/isList}}{{^isList}}kotlin.Array{{/isList}}<{{classname}}.{{{nameInCamelCase}}}>{{/isListContainer}}{{^isListContainer}}{{classname}}.{{{nameInCamelCase}}}{{/isListContainer}}{{/isEnum}}{{^isEnum}}{{{dataType}}}{{/isEnum}}{{#isNullable}}?{{/isNullable}}

modules/openapi-generator/src/main/resources/kotlin-client/jvm-common/infrastructure/Serializer.kt.mustache

@@ -24,6 +24,7 @@ import java.util.UUID
 {{/gson}}
 {{#jackson}}
 import com.fasterxml.jackson.databind.ObjectMapper
+import com.fasterxml.jackson.databind.SerializationFeature
 import com.fasterxml.jackson.datatype.jdk8.Jdk8Module
 import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule
 import com.fasterxml.jackson.annotation.JsonInclude
@@ -70,5 +71,6 @@ import java.util.Date
         .registerModule(Jdk8Module())
         .registerModule(JavaTimeModule())
         .setSerializationInclusion(JsonInclude.Include.NON_ABSENT)
+        .configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false)
 {{/jackson}}
 }

modules/openapi-generator/src/main/resources/kotlin-client/typeInfoAnnotation.mustache

@@ -0,0 +1,6 @@
+@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "{{{discriminator.propertyBaseName}}}", visible = true)
+@JsonSubTypes(
+{{#discriminator.mappedModels}}
+    JsonSubTypes.Type(value = {{modelName}}::class, name = "{{^vendorExtensions.x-discriminator-value}}{{mappingName}}{{/vendorExtensions.x-discriminator-value}}{{#vendorExtensions.x-discriminator-value}}{{{vendorExtensions.x-discriminator-value}}}{{/vendorExtensions.x-discriminator-value}}"){{^-last}},{{/-last}}
+{{/discriminator.mappedModels}}
+)