[FIR] Implement FirReturnAllowedChecker

Supported diagnostics:
- RETURN_NOT_ALLOWED
- RETURN_IN_FUNCTION_WITH_EXPRESSION_BODY

compiler/testData/diagnostics/tests/functionAsExpression/AutoLabels.fir.kt

@@ -7,5 +7,5 @@ fun autolabel(l: List<Int>) = l.map (fun (i: Int): Int {
 })
 
 fun unresolvedMapLabel(l: List<Int>) = l.map (l@ fun(i: Int): Int {
-    return@map 4
+    <!RETURN_NOT_ALLOWED!>return@map<!> 4
 })

compiler/testData/diagnostics/tests/functionAsExpression/ForbiddenNonLocalReturn.fir.kt

@@ -1,22 +0,0 @@
-// !DIAGNOSTICS: -UNUSED_VARIABLE
-
-fun test() {
-    fun bar() {
-        val bas = fun() {
-            return@bar
-        }
-    }
-
-    val bar = fun() {
-        return@test
-    }
-}
-
-fun foo() {
-    val bal = bag@ fun () {
-        val bar = fun() {
-            return@bag
-        }
-        return@bag
-    }
-}

compiler/testData/diagnostics/tests/functionAsExpression/ForbiddenNonLocalReturn.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // !DIAGNOSTICS: -UNUSED_VARIABLE
 
 fun test() {