enable babel-loader cache

[silverwind]

This speeds up repeated webpack builds by around 20%. It will use the default cache directory node_modules/.cache/babel-loader.

[silverwind]

One invalidation issue to be aware of is babel/babel-loader#690. It could probably be worked around via make:

node_modules/.cache/babel-loader: package-lock.json
  rm -rf $@
  mkdir -p $@

$(WEBPACK_DEST): $(WEBPACK_SOURCES) | node_modules node_modules/.cache/babel-loader

[codecov-io]

Codecov Report

Merging #10083 into master will increase coverage by <.01%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master   #10083      +/-   ##
==========================================
+ Coverage   43.45%   43.45%   +<.01%     
==========================================
  Files         566      566              
  Lines       78987    78989       +2     
==========================================
+ Hits        34322    34324       +2     
- Misses      40427    40429       +2     
+ Partials     4238     4236       -2

Impacted Files	Coverage Δ
services/pull/pull.go	33.93% <0%> (ø)	⬆️
routers/repo/branch.go	55.72% <100%> (+0.34%)	⬆️
models/unit.go	37.03% <0%> (-2.47%)	⬇️
modules/log/event.go	64.61% <0%> (-1.03%)	⬇️
routers/repo/view.go	38.59% <0%> (-0.88%)	⬇️
services/pull/patch.go	67.92% <0%> (ø)	⬆️
models/repo.go	51.46% <0%> (+0.13%)	⬆️
services/pull/temp_repo.go	34.18% <0%> (+2.56%)	⬆️
modules/process/manager.go	78.31% <0%> (+3.61%)	⬆️

---

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[silverwind]

Cache invalidation added for changes to package.json or package-lock.json.
Also added webpack.config.js as a prereq to the webpack step as well.

[silverwind]

Rewrote cache invalidation to use cacheIdentifier option and not depend on make any more.