FIR checker: warn useless as and is

compiler/testData/diagnostics/tests/IsExpressions.fir.kt

@@ -1,21 +1,21 @@
 // FILE: KotlinFile.kt
 
 fun test() {
-   if (1 is Int) {
+   if (<!USELESS_IS_CHECK!>1 is Int<!>) {
      if (1 is Boolean) {
 
      }
    }
 
    A.create() is A
-   A.create() is A?
+   <!USELESS_IS_CHECK!>A.create() is A?<!>
 
    <!UNRESOLVED_REFERENCE!>unresolved<!> is A
    <!UNRESOLVED_REFERENCE!>unresolved<!> is A?
 
    val x = foo()
    x as String
-   x is String
+   <!USELESS_IS_CHECK!>x is String<!>
 }
 
 fun foo(): Any = ""
@@ -23,4 +23,4 @@ fun foo(): Any = ""
 // FILE: A.java
 class A {
     static A create() { return null; }
-}
+}