Regular modifier checker implemented (initial version). A set of tests fixed accordingly.

Most of modifier diagnostic is expressed by REDUNDANT_MODIFIER, INCOMPATIBLE_MODIFIERS, REPEATED_MODIFIER, WRONG_MODIFIER_TARGET, WRONG_MODIFIER_PARENT.
A set of modifier diagnostics is not in use now (but not deleted yet).

compiler/testData/diagnostics/tests/classObjects/ClassObjects.kt

@@ -26,7 +26,7 @@ class B() {
 }
 
 object b {
-  <!COMPANION_OBJECT_NOT_ALLOWED!>companion<!> object {
+  <!WRONG_MODIFIER_CONTAINING_DECLARATION!>companion<!> object {
     val x = 1
   } // error
 }