FIR checker: report UNSAFE_CALL for overloaded function calls

Previously if an unsafe call is to an overloaded function, FIR checkers
report NONE_APPLICABLE. This change instead report them as UNSAFE_CALL
or its variants.

compiler/testData/diagnostics/tests/nullabilityAndSmartCasts/kt2216.fir.kt

@@ -16,7 +16,7 @@ fun foo() {
     val y: Int? = 0
     val z: Int? = 0
     bar(<!ARGUMENT_TYPE_MISMATCH!>if (y != null) y else z<!>, <!ARGUMENT_TYPE_MISMATCH!>y<!>)
-    y <!NONE_APPLICABLE!>+<!> 2
+    y <!UNSAFE_OPERATOR_CALL!>+<!> 2
     baz(<!ARGUMENT_TYPE_MISMATCH!>y<!>, <!ARGUMENT_TYPE_MISMATCH!>y<!>, if (y == null) return else y, y)
     baz(y, z!!, z, y)
 }