reduce webpack build time by 55% with this one simple trick

[cezaraugusto]

This make use of cache option for babel-loader which is huge by itself

close #11473
Auditors: @bsclifton, @evq

tests has a margin of sampling error of plus or minus ~300ms

• main bundle down from ~2.7s to ~1.3s
• devtools bundle down from ~1.9s to ~1.5s
• webtorrent bundle down from ~2.1s to ~0.9s

Verbose:

with cache

⚡️	main bundle	devtools bundle	webtorrent bundle
1st try	13946ms	14816ms	8718ms
2nd try	14840ms	15693ms	9361ms
3rd try	14842ms	15685ms	9830ms

without cache

💩	main bundle	devtools bundle	webtorrent bundle
1st try	28841ms	19936ms	22718ms
2nd try	28845ms	18899ms	21738ms
3rd try	26166ms	19773ms	20894ms

Test Plan:

• Try running npm run watch and look for time hint in webpack stats
• You should still be able to make changes and they should hot-reaload as usual

[luixxiul]

with this one simple trick

Finally 🏁😄

[luixxiul]

LGTM :-)

[bsclifton]

++ nice find! 😄