FIR: fix label stealling and crash with multiple labels

Consider the code below

```
fun test() {
  a@ b@ {
    {}
  }
}
```

Currently when the code is converted to FIR, label `b` is bound to the
outer lambda and `a` gets bound to the inner lambda because it's not
consumed. This is wrong and also leads transfromation to fail with
exceptions because of the unexpected consumption of `a`.

This change fixes the above issue by designating a specific node in the
AST as the allowed user of a label when the label is added.

compiler/testData/diagnostics/tests/controlStructures/notAFunctionLabel_before.txt

@@ -9,6 +9,7 @@ public fun testLambdaLabel(): () -> kotlin.Unit
 public fun testLambdaMultipleLabels1(): () -> kotlin.Unit
 public fun testLambdaMultipleLabels2(): () -> kotlin.Unit
 public fun testLoopLabelInReturn(/*0*/ xs: kotlin.collections.List<kotlin.Int>): kotlin.Unit
+public fun testMultipleLabelsWithNestedLambda(): kotlin.Unit
 public fun testParenthesizedLambdaLabel(): () -> kotlin.Unit
 public fun testValLabelInReturn(): kotlin.Unit
 
@@ -18,3 +19,4 @@ public fun testValLabelInReturn(): kotlin.Unit
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 }
+