This pr introduces some cargo features. For `swc_common` and `swc_ecma_ast`, it introduces a feature flag `fold`.
`Fold` and `Visit` traits exist only if the feature is enabled.
For `swc_ecma_parser`, flag called `verify` is added. When disabled, we skip checking of validity of some expressions.
e.g. `{foo = bar}`
Verification is disabled by default it requires nightly compiler
`Map<T>` adds a method named `map` which is actually `Box<T>` -> `Box<T>` without reallocation.
swc_ecma_transforms:
- chain_at!(Type, passes)
This macro deeply joins path at 'Type' level.
