* Use file hashes instead of BUILD_ID.
Now JSON pages also not prefixed with a hash and
doesn't support immutable caching.
Instead it supports Etag bases caching.
* Remove appUpdated Router Events hook.
Becuase now we don't need it because there's no buildId validation.
* Remove buildId generation.
* Turn off hash checks in the dev mode.
* Update tests.
* Revert "Remove buildId generation."
This reverts commit fdd36a5a0a307becdbd1d85ae3881b3a15b03d26.
* Bring back the buildId validation.
* Handle buildId validation only in production.
* Add BUILD_ID to path again.
* Remove duplicate immutable header.
* Fix tests.
* Write BUILD_ID when building.
It's a random id (uuid.v4())
* Add buildId to the core JS files.
* Add immutable cache-control header.
Only if the buildId is matched.
* Set '-' as the dev buildId always.
* Add buildId handling for JSON pages.
* Add AOT gzip content-encoding support.
Currently we only do this for
main.js and commons.js only.
* Remove unwanted await.
* Use Promise.all to gzip assets in parallel.
* compile _document using webpack
* don't emit the bundle file of _document.js
* exclude _document.js from minChunks of CommonsChunkPlugin
* handle creation/removal of pages/_document.js
* improve path handlings
