Improve Kotlin extensions doc about type erasure

Since type erasure can be fixed only when using
ParameterizedTypeReference based Java methods, RestOperations and
WebFlux API documentation should be updated to specify which extensions
are subject to type erasure, and which are not.

Issue: SPR-16273

spring-webflux/src/main/kotlin/org/springframework/web/reactive/function/client/ClientResponseExtensions.kt

@@ -23,7 +23,8 @@ import reactor.core.publisher.Mono
 
 /**
  * Extension for [ClientResponse.bodyToMono] providing a `bodyToMono<Foo>()` variant
- * leveraging Kotlin reified type parameters.
+ * leveraging Kotlin reified type parameters. This extension is not subject to type
+ * erasure and retains actual generic type arguments.
  *
  * @author Sebastien Deleuze
  * @since 5.0
@@ -33,7 +34,8 @@ inline fun <reified T : Any> ClientResponse.bodyToMono(): Mono<T> =
 
 /**
  * Extension for [ClientResponse.bodyToFlux] providing a `bodyToFlux<Foo>()` variant
- * leveraging Kotlin reified type parameters.
+ * leveraging Kotlin reified type parameters. This extension is not subject to type
+ * erasure and retains actual generic type arguments.
  *
  * @author Sebastien Deleuze
  * @since 5.0
@@ -43,7 +45,8 @@ inline fun <reified T : Any> ClientResponse.bodyToFlux(): Flux<T> =
 
 /**
  * Extension for [ClientResponse.toEntity] providing a `toEntity<Foo>()` variant
- * leveraging Kotlin reified type parameters.
+ * leveraging Kotlin reified type parameters. This extension is not subject to type
+ * erasure and retains actual generic type arguments.
  *
  * @author Sebastien Deleuze
  * @since 5.0
@@ -53,7 +56,8 @@ inline fun <reified T : Any> ClientResponse.toEntity(): Mono<ResponseEntity<T>>
 
 /**
  * Extension for [ClientResponse.toEntityList] providing a `bodyToEntityList<Foo>()` variant
- * leveraging Kotlin reified type parameters.
+ * leveraging Kotlin reified type parameters. This extension is not subject to type
+ * erasure and retains actual generic type arguments.
  *
  * @author Sebastien Deleuze
  * @since 5.0

spring-webflux/src/main/kotlin/org/springframework/web/reactive/function/client/WebClientExtensions.kt

@@ -25,7 +25,8 @@ import reactor.core.publisher.Mono
 
 /**
  * Extension for [WebClient.RequestBodySpec.body] providing a `body<Foo>()` variant
- * leveraging Kotlin reified type parameters.
+ * leveraging Kotlin reified type parameters. This extension is not subject to type
+ * erasure and retains actual generic type arguments.
  *
  * @author Sebastien Deleuze
  * @since 5.0
@@ -36,7 +37,8 @@ inline fun <reified T : Any, S : Publisher<T>> RequestBodySpec.body(publisher: S
 
 /**
  * Extension for [WebClient.ResponseSpec.bodyToMono] providing a `bodyToMono<Foo>()` variant
- * leveraging Kotlin reified type parameters.
+ * leveraging Kotlin reified type parameters. This extension is not subject to type
+ * erasure and retains actual generic type arguments.
  *
  * @author Sebastien Deleuze
  * @since 5.0
@@ -47,7 +49,8 @@ inline fun <reified T : Any> WebClient.ResponseSpec.bodyToMono(): Mono<T> =
 
 /**
  * Extension for [WebClient.ResponseSpec.bodyToFlux] providing a `bodyToFlux<Foo>()` variant
- * leveraging Kotlin reified type parameters.
+ * leveraging Kotlin reified type parameters. This extension is not subject to type
+ * erasure and retains actual generic type arguments.
  *
  * @author Sebastien Deleuze
  * @since 5.0

spring-webflux/src/main/kotlin/org/springframework/web/reactive/function/server/ServerRequestExtensions.kt

@@ -22,7 +22,8 @@ import reactor.core.publisher.Mono
 
 /**
  * Extension for [ServerRequest.bodyToMono] providing a `bodyToMono<Foo>()` variant
- * leveraging Kotlin reified type parameters.
+ * leveraging Kotlin reified type parameters. This extension is not subject to type
+ * erasure and retains actual generic type arguments.
  * 
  * @author Sebastien Deleuze
  * @since 5.0
@@ -32,7 +33,8 @@ inline fun <reified T : Any> ServerRequest.bodyToMono(): Mono<T> =
 
 /**
  * Extension for [ServerRequest.bodyToFlux] providing a `bodyToFlux<Foo>()` variant
- * leveraging Kotlin reified type parameters.
+ * leveraging Kotlin reified type parameters. This extension is not subject to type
+ * erasure and retains actual generic type arguments.
  *
  * @author Sebastien Deleuze
  * @since 5.0

spring-webflux/src/main/kotlin/org/springframework/web/reactive/function/server/ServerResponseExtensions.kt

@@ -22,7 +22,9 @@ import org.springframework.http.MediaType
 import reactor.core.publisher.Mono
 
 /**
- * Extension for [ServerResponse.BodyBuilder.body] providing a `body(Publisher<T>)` variant.
+ * Extension for [ServerResponse.BodyBuilder.body] providing a `body(Publisher<T>)`
+ * variant. This extension is not subject to type erasure and retains actual generic
+ * type arguments.
  *
  * @author Sebastien Deleuze
  * @since 5.0
@@ -31,7 +33,9 @@ inline fun <reified T : Any> ServerResponse.BodyBuilder.body(publisher: Publishe
 		body(publisher, object : ParameterizedTypeReference<T>() {})
 
 /**
- * Extension for [ServerResponse.BodyBuilder.body] providing a `bodyToServerSentEvents(Publisher<T>)` variant.
+ * Extension for [ServerResponse.BodyBuilder.body] providing a
+ * `bodyToServerSentEvents(Publisher<T>)` variant. This extension is not subject to type
+ * erasure and retains actual generic type arguments.
  *
  * @author Sebastien Deleuze
  * @since 5.0