Support warning about useless cast on safe cast

#KT-13348 Fixed

compiler/testData/diagnostics/tests/smartCasts/alwaysNull.kt

@@ -16,7 +16,7 @@ fun String?.gav() {}
 fun bar(s: String?) {
     if (s != null) return
     <!DEBUG_INFO_CONSTANT!>s<!>.gav()
-    <!DEBUG_INFO_CONSTANT!>s<!> as? String
+    <!DEBUG_INFO_CONSTANT!>s<!> <!USELESS_CAST!>as? String<!>
     <!DEBUG_INFO_CONSTANT!>s<!> <!USELESS_CAST!>as String?<!>
     <!ALWAYS_NULL!>s<!> as String
 }

compiler/testData/diagnostics/tests/smartCasts/extensionSafeCall.kt

@@ -7,7 +7,7 @@ fun <T> T?.let(f: (T) -> Unit) {
 }
 
 fun test(your: Your?) {
-    (your?.foo() as? Any)?.let {}
+    (your?.foo() <!USELESS_CAST!>as? Any<!>)?.let {}
     // strange smart cast to 'Your' at this point
     your<!UNSAFE_CALL!>.<!>hashCode()
 }

compiler/testData/diagnostics/tests/smartCasts/safeAs.kt

@@ -1,13 +1,13 @@
 // See also KT-10992: we should have no errors for all unsafe hashCode() calls
 
 fun foo(arg: Any?) {
-    val x = arg as? Any ?: return
+    val x = arg <!USELESS_CAST!>as? Any<!> ?: return
     <!DEBUG_INFO_SMARTCAST!>arg<!>.hashCode()
     x.hashCode()
 }
 
 fun bar(arg: Any?) {
-    arg as? Any ?: return
+    arg <!USELESS_CAST!>as? Any<!> ?: return
     <!DEBUG_INFO_SMARTCAST!>arg<!>.hashCode()
 }