[FIR] Implement FirReturnAllowedChecker

Supported diagnostics:
- RETURN_NOT_ALLOWED
- RETURN_IN_FUNCTION_WITH_EXPRESSION_BODY

compiler/testData/diagnostics/tests/controlStructures/notAFunctionLabel_after.fir.kt

@@ -31,7 +31,7 @@ fun testAnnotatedLambdaLabel() =
 
 fun testLambdaMultipleLabels1() =
     lambda1@ lambda2@ {
-        return@lambda1
+        <!RETURN_NOT_ALLOWED!>return@lambda1<!>
     }
 
 fun testLambdaMultipleLabels2() =
@@ -46,7 +46,7 @@ fun testAnonymousFunctionLabel() =
 
 fun testLoopLabelInReturn(xs: List<Int>) {
     L@ for (x in xs) {
-        if (x > 0) return@L
+        if (x > 0) <!RETURN_NOT_ALLOWED!>return@L<!>
     }
 }
 
@@ -59,4 +59,4 @@ fun testHighOrderFunctionCallLabelInReturn() {
     L@ run {
         return@L
     }
-}
+}