Add Kotlin WebClient extensions

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

@@ -0,0 +1,13 @@
+package org.springframework.web.reactive.function.client
+
+import org.reactivestreams.Publisher
+
+/**
+ * Extension for [WebClient.HeaderSpec.exchange] providing a variant without explicit class
+ * parameter thanks to Kotlin reified type parameters.
+ *
+ * @author Sebastien Deleuze
+ * @since 5.0
+ */
+inline fun <reified T : Any, S : Publisher<T>> WebClient.HeaderSpec.exchange(publisher: S) =
+        exchange(publisher, T::class.java)