JetDiagnosticsTest migrated to TestGenerator

- test data files renamed from *.jet to *.kt

compiler/testData/diagnostics/tests/scopes/kt1244.kt

@@ -0,0 +1,13 @@
+//KT-1244 Frontend allows access to private members of other classes
+
+package kt1244
+
+class A {
+    private var a = ""
+}
+
+class B() {
+    {
+        A().<!INVISIBLE_MEMBER!>a<!> = "Hello"
+    }
+}