enhancement(transformer): Add helper function to extract the first identifier of a BindingName

E.g.:

```
const [[[[[var]]]]] = ...
```

Author: martinjlowm

src/transformer/descriptor/helper/helper.ts

@@ -17,6 +17,22 @@ export namespace TypescriptHelper {
     | ts.SyntaxKind.UndefinedKeyword;
   }
 
+  export function ExtractFirstIdentifier(bindingName: ts.BindingName): ts.Identifier {
+    let identifier: ts.BindingName = bindingName;
+    let saneSearchLimit: number = 10;
+
+    while (!ts.isIdentifier(identifier)) {
+      const [bindingElement]: Array<ts.BindingElement | undefined> = (identifier.elements as ts.NodeArray<ts.ArrayBindingElement>).filter(ts.isBindingElement);
+      if (!bindingElement || !--saneSearchLimit) {
+        throw new Error('Failed to find an identifier for the primary declaration!');
+      }
+
+      identifier = bindingElement.name;
+    }
+
+    return identifier;
+  }
+
   export function IsLiteralOrPrimitive(typeNode: ts.Node): typeNode is PrimitiveTypeNode {
     switch (typeNode.kind) {
       case ts.SyntaxKind.LiteralType: