Destructuring consistency fixes (#1417)

- Use AST_Destructuring for lhf assignment patterns
- Use AST_DefaultAssign for default assignments
- Add more checks for lhs expressions
- Add lots of testing
- Cleanup ast (e.g. remove default property)
- Fix #1402 based on a patch from @kzc
- Refine spread allowance in array destructring pattern
- Add destructuring AST tree checker

test/compress/template-string.js

@@ -376,4 +376,4 @@ template_ending_with_newline: {
 `;
         };
     } expect_exact: "function foo(e){return`this is a template string!\n`}"
-}
+}