Introduce new naming convention for captured receiver backing fields

'receiver$0' -> '$this_<label>'

compiler/testData/codegen/asmLike/receiverMangling/innerClass.txt

@@ -0,0 +1,9 @@
+public final class Foo$Bar : java/lang/Object {
+    final Foo this$0
+
+    public void <init>(Foo $outer)
+}
+
+public final class Foo : java/lang/Object {
+    public void <init>()
+}