Tests for diagnostics on this and super are moved and broken into smaller parts

compiler/testData/diagnostics/tests/thisAndSuper/thisInNestedClasses.kt

@@ -0,0 +1,9 @@
+class A(val a:Int) {
+
+  class B() {
+    val x = this@B : B
+    val y = this@A : A
+    val z = this : B
+    val Int.xx : Int get() = this : Int
+  }
+}