Add tests for obsolete issues

#KT-4628 Obsolete
 #KT-3897 Obsolete
 #KT-3898 Obsolete
 #KT-7523 Obsolete

compiler/testData/diagnostics/tests/j+k/brokenCode/classDuplicates.kt

@@ -0,0 +1,13 @@
+// FILE: Hello.kt
+private class Hello()
+{
+    val a = 4
+}
+
+fun test() {
+    // no exception is thrown (see KT-3897)
+    Hello().a
+}
+
+// FILE: Hello.java
+public class Hello {}