Introduce ServerRequest.methodName()

This commit introduces a methodName() method to the ServerRequest,
returning the String name of the method. This method is useful for
non-standard HTTP methods.

spring-test/src/main/java/org/springframework/mock/web/reactive/function/server/MockServerRequest.java

@@ -109,6 +109,11 @@ public class MockServerRequest implements ServerRequest {
 		return this.method;
 	}
 
+	@Override
+	public String methodName() {
+		return this.method.name();
+	}
+
 	@Override
 	public URI uri() {
 		return this.uri;