FIR checker: warn useless as and is

compiler/testData/diagnostics/tests/cast/IsErasedUpcastToNonReified.fir.kt

@@ -1,14 +1,14 @@
 fun <T, S : T> test(x: T?, y: S, z: T) {
     x is T
-    x is T?
+    <!USELESS_IS_CHECK!>x is T?<!>
 
-    y is T
-    y is S
-    y is T?
-    y is S?
+    <!USELESS_IS_CHECK!>y is T<!>
+    <!USELESS_IS_CHECK!>y is S<!>
+    <!USELESS_IS_CHECK!>y is T?<!>
+    <!USELESS_IS_CHECK!>y is S?<!>
 
-    z is T
-    z is T?
+    <!USELESS_IS_CHECK!>z is T<!>
+    <!USELESS_IS_CHECK!>z is T?<!>
 
     null as T
     null as T?
@@ -22,6 +22,6 @@ inline fun <reified T> test(x: T?) {
 }
 
 fun <T> foo(x: List<T>, y: List<T>?) {
-    x is List<T>
+    <!USELESS_IS_CHECK!>x is List<T><!>
     y is List<T>
-}
+}