Highlighting "as Foo" for useless casts in gray.

#KT-6070 fixed

compiler/testData/diagnostics/tests/cast/bare/FromErrorType.kt

@@ -1,6 +1,6 @@
 class G<T>
 
 fun foo(p: <!UNRESOLVED_REFERENCE!>P<!>) {
-    val v = <!DEBUG_INFO_ELEMENT_WITH_ERROR_TYPE!>p<!> <!USELESS_CAST_STATIC_ASSERT_IS_FINE!>as<!> <!NO_TYPE_ARGUMENTS_ON_RHS!>G?<!>
+    val v = <!DEBUG_INFO_ELEMENT_WITH_ERROR_TYPE!>p<!> <!USELESS_CAST_STATIC_ASSERT_IS_FINE!>as <!NO_TYPE_ARGUMENTS_ON_RHS!>G?<!><!>
     v!!: G<*>
 }

compiler/testData/diagnostics/tests/cast/bare/ToErrorType.kt

@@ -1,6 +1,6 @@
 class P
 
 fun foo(p: P): Any {
-    val v = p <!USELESS_CAST_STATIC_ASSERT_IS_FINE!>as<!> <!UNRESOLVED_REFERENCE!>G<!>
+    val v = p <!USELESS_CAST_STATIC_ASSERT_IS_FINE!>as <!UNRESOLVED_REFERENCE!>G<!><!>
     return <!DEBUG_INFO_ELEMENT_WITH_ERROR_TYPE!>v<!>
 }