KT-22274 report warning on labels that can't be referenced

Labels are meaningful only if they can be referenced by 'break',
'continue', or 'return' expressions.

compiler/testData/diagnostics/tests/controlFlowAnalysis/deadCode/commentsInDeadCode.kt

@@ -12,7 +12,7 @@ fun test2() {
     <!UNREACHABLE_CODE!>bar(<!>11, todo()/*comment1*/, <!UNREACHABLE_CODE!>""/*comment2*/)<!>
 }
 fun test3() {
-    <!UNREACHABLE_CODE!>bar(<!>11, l@(todo()/*comment*/), <!UNREACHABLE_CODE!>"")<!>
+    <!UNREACHABLE_CODE!>bar(<!>11, <!REDUNDANT_LABEL_WARNING!>l@<!>(todo()/*comment*/), <!UNREACHABLE_CODE!>"")<!>
 }
 
 fun todo(): Nothing = throw Exception()