Prohibit objects inside inner classes

#KT-16232 Fixed

compiler/testData/diagnostics/tests/inner/nestedObject.kt

@@ -0,0 +1,12 @@
+// SKIP_TXT
+class Outer {
+    inner class Inner1 {
+        <!NESTED_OBJECT_NOT_ALLOWED!>object Obj1<!>
+
+        <!WRONG_MODIFIER_CONTAINING_DECLARATION!>companion<!> object Obj2
+
+        inner class Inner2 {
+            <!NESTED_OBJECT_NOT_ALLOWED!>object Obj3<!>
+        }
+    }
+}