Support Kotlin extensions in web handlers

This commit restores support for Kotlin extensions in
web handlers, and adds support for invoking reflectively
suspending extension functions, as well as the other
features supported as of Spring Framework 6.1 like
value classes and default value for parameters.

Closes gh-31876

spring-web/src/test/kotlin/org/springframework/web/method/support/InvocableHandlerMethodKotlinTests.kt

@@ -104,6 +104,22 @@ class InvocableHandlerMethodKotlinTests {
 		Assertions.assertThat(value).isEqualTo("foo")
 	}
 
+	@Test
+	fun extension() {
+		composite.addResolver(StubArgumentResolver(CustomException::class.java, CustomException("foo")))
+		val value = getInvocable(ExtensionHandler::class.java, CustomException::class.java).invokeForRequest(request, null)
+		Assertions.assertThat(value).isEqualTo("foo")
+	}
+
+	@Test
+	fun extensionWithParameter() {
+		composite.addResolver(StubArgumentResolver(CustomException::class.java, CustomException("foo")))
+		composite.addResolver(StubArgumentResolver(Int::class.java, 20))
+		val value = getInvocable(ExtensionHandler::class.java, CustomException::class.java, Int::class.java)
+			.invokeForRequest(request, null)
+		Assertions.assertThat(value).isEqualTo("foo-20")
+	}
+
 	private fun getInvocable(clazz: Class<*>, vararg argTypes: Class<*>): InvocableHandlerMethod {
 		val method = ResolvableMethod.on(clazz).argTypes(*argTypes).resolveMethod()
 		val handlerMethod = InvocableHandlerMethod(clazz.constructors.first().newInstance(), method)
@@ -150,10 +166,23 @@ class InvocableHandlerMethodKotlinTests {
 			get() = "foo"
 	}
 
+	private class ExtensionHandler {
+
+		fun CustomException.handle(): String {
+			return "${this.message}"
+		}
+
+		fun CustomException.handleWithParameter(limit: Int): String {
+			return "${this.message}-$limit"
+		}
+	}
+
 	@JvmInline
 	value class LongValueClass(val value: Long)
 
 	@JvmInline
 	value class DoubleValueClass(val value: Double)
 
+	class CustomException(message: String) : Throwable(message)
+
 }