Investigate whether babel-loader 'cacheCompression: false' can improve performance

[edmorley]

In babel-loader 8.0.2, a new cacheCompression option has been added (babel/babel-loader#574), which can be used to disable the default behaviour of gzip-compressing the babel-loader cache. Disabling the compression resulted in a small performance improvement for that project (at the expense of an increase in disk usage).

I tried locally with Treeherder and saw a 200-300ms improvement in build times (this was with an SSD), with the cache size on disk increasing from 0.7MB to 2.5MB. We should try with a few different projects, and also in CI (where I/O is likely slower) to confirm that disabling it is generally a performance win.

[edmorley]

CRA now disables it during development (only):
facebook/create-react-app#5053

[edmorley]

Without knowing users disk and/or CPU speeds, it seems like it will be hard for us to pick a suitable value for all use-cases here. As such I think it might be best to just stick with the babel-loader default (particularly since webpack 5's new cache probably makes this redundant).