[FIR] Fix missing USELESS_CAST

`FirUselessTypeOperationCallChecker` always checks exact types matching for `as` operator

Simplify code of cast checker and utils

^KT-56629 Fixed
^KT-56615 Fixed
^KT-59820 Fixed

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

@@ -15,7 +15,7 @@ fun test(x: Int?) {
     foo(x as? Number)
 
     if (x is Int) {
-        val b = x as? Int
+        val b = x <!USELESS_CAST!>as? Int<!>
     }
 }