build: improve webpack configs for npm link

[ktmud]

SUMMARY

I noticed that sometimes Webpack will not use the source files of @superset-ui/core when is it installed via npm link.

This change should fix it.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

N/A

TEST PLAN

Test locally.

1. npm link both the core package and a plugin package.
2. Start npm dev-server.
3. Go to Chrome Dev Tools "Sources" panal, use Cmd + p to search for files.
4. You should see files from superset-ui/core/src instead of superset-ui/core/esm.

[codecov-io]

Codecov Report

Merging #12313 (7ede370) into master (6df8224) will decrease coverage by 4.15%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #12313      +/-   ##
==========================================
- Coverage   67.15%   62.99%   -4.16%     
==========================================
  Files        1002     1002              
  Lines       49265    49286      +21     
  Branches     5003     5010       +7     
==========================================
- Hits        33082    31049    -2033     
- Misses      16060    18035    +1975     
- Partials      123      202      +79     

Flag	Coverage Δ
cypress	?
javascript	61.20% <ø> (-0.02%)	⬇️
python	64.16% <ø> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
superset-frontend/src/SqlLab/App.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/explore/App.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/dashboard/App.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/setup/setupColors.js	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/chart/ChartContainer.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/explore/reducers/index.js	0.00% <0.00%> (-100.00%)	⬇️
...et-frontend/src/dashboard/containers/Dashboard.jsx	0.00% <0.00%> (-100.00%)	⬇️
...t-frontend/src/dashboard/containers/SliceAdder.jsx	0.00% <0.00%> (-100.00%)	⬇️
...t-frontend/src/explore/reducers/getInitialState.js	0.00% <0.00%> (-100.00%)	⬇️
...-frontend/src/visualizations/presets/MainPreset.js	0.00% <0.00%> (-100.00%)	⬇️
... and 197 more

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[rusackas]

This is awesome!!!!

[villebro]

Thanks for fixing this, works perfectly now!