replaced double underscore as new standard way of writing the dummy annotation for onX instead of single underscore, which emits warnings on javac8+.

Also made dollars and Xes legal in addition to underscores, in case double underscore disappears later too.

test/transform/resource/before/Constructors.java

@@ -10,7 +10,7 @@
 	final int x;
 	String name;
 }
-@lombok.RequiredArgsConstructor(onConstructor=@_(@Deprecated)) class RequiredArgsConstructorWithAnnotations {
+@lombok.RequiredArgsConstructor(onConstructor=@__(@Deprecated)) class RequiredArgsConstructorWithAnnotations {
 	final int x;
 	String name;
 }