Add Kotlin extension functions for ClientResponseField

In gh-1331, several Kotlin extensions functions were added for
`GraphQlClient` specs. This commit adds missing extension functions for
`ClientResponseField`.

Closes gh-1393

Author: bclozel

spring-graphql/src/main/kotlin/org/springframework/graphql/client/ClientResponseFieldExtensions.kt

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2025-present the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.graphql.client
+
+import org.springframework.core.ParameterizedTypeReference
+
+/**
+ * Extension for [ClientResponseField.toEntity] providing a `toEntity<Book>()` variant
+ * leveraging Kotlin reified type parameters. This extension is not subject to type
+ * erasure and retains actual generic type arguments.
+ *
+ * @author Brian Clozel
+ * @since 2.0.1
+ */
+inline fun <reified T : Any> ClientResponseField.toEntity(): T? =
+    toEntity(object : ParameterizedTypeReference<T>() {})
+
+/**
+ * Extension for [ClientResponseField.toEntityList] providing a `toEntityList<Book>()` variant
+ * leveraging Kotlin reified type parameters. This extension is not subject to type
+ * erasure and retains actual generic type arguments.
+ *
+ * @author Brian Clozel
+ * @since 2.0.1
+ */
+inline fun <reified T : Any> ClientResponseField.toEntityList(): List<T> =
+    toEntityList(object : ParameterizedTypeReference<T>() {})

spring-graphql/src/main/kotlin/org/springframework/graphql/client/GraphQlClientExtensions.kt

@@ -84,4 +84,4 @@ inline fun <reified T : Any> GraphQlClient.RetrieveSubscriptionSpec.toEntity():
  * @since 2.0.0
  */
 inline fun <reified T : Any> GraphQlClient.RetrieveSubscriptionSpec.toEntityList(): Flux<List<T>> =
-    toEntityList(object : ParameterizedTypeReference<T>() {})
+    toEntityList(object : ParameterizedTypeReference<T>() {})

spring-graphql/src/test/kotlin/org/springframework/graphql/client/GraphQlClientExtensionsTests.kt

@@ -75,4 +75,4 @@ class GraphQlClientExtensionsTests {
 
     private class Book
 
-}
+}

spring-graphql/src/test/kotlin/org/springframework/graphql/client/GraphQlResponseFieldExtensionsTests.kt

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2025-present the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.graphql.client
+
+import io.mockk.mockk
+import io.mockk.verify
+import org.junit.jupiter.api.Test
+import org.springframework.core.ParameterizedTypeReference
+
+
+/**
+ * Tests for [ClientResponseField] Kotlin extensions.
+ *
+ * @author Brian Clozel
+ */
+class GraphQlResponseFieldExtensionsTests {
+
+    private val responseField = mockk<ClientResponseField>(relaxed = true)
+
+    @Test
+    fun `ClientResponseField#toEntity with reified type parameters`() {
+        responseField.toEntity<Map<String, Book>>()
+        verify { responseField.toEntity(object : ParameterizedTypeReference<Map<String, Book>>() {}) }
+    }
+
+    @Test
+    fun `ClientResponseField#toEntityList with reified type parameters`() {
+        responseField.toEntityList<Book>()
+        verify { responseField.toEntityList(object : ParameterizedTypeReference<Book>() {}) }
+    }
+
+    private class Book
+
+}