* Remove CanIUse trait, which will be reimpplemented in future
using Visitor.
* Remove some other unused stuffs.
* Change public path of swc_common::fold::* to swc_common::*.
- Parser and lexer for lastest ecma spec https://tc39.github.io/ecma262
- Lexer is currently very inefficient
- Use https://github.com/tc39/test262-parser-tests/ for testing.
- Implement proc-macro based ast folder and assert_eq_ignore_span! based on it.
- Some utilities for proc macro at /macros/common
