[DX] Add per-package Yarn scripts (build, watch, test, lint, ...)

[Kocal]

Q	A
Bug fix?	no
New feature?	no
Issues	Fix #...
License	MIT

When working in UX Map, it was very painful to build or watch modifications on .ts files, I had investigate how the building process worked, and had to run Rollup like this, which is far from ideal (not documented and not obvious):

./node_modules/.bin/rollup -c --environment INPUT_FILE:src/Map/assets/src/abstract_map_controller.ts -w
./node_modules/.bin/rollup -c --environment INPUT_FILE:src/Map/src/Bridge/Google/assets/src/map_controller.ts -w
./node_modules/.bin/rollup -c --environment INPUT_FILE:src/Map/src/Bridge/Leaflet/assets/src/map_controller.ts -w

And I also felt sorry for @rrr63 when he worked on adding Polygons on Map (#2162)...

This PR improves the way developers will work on UX, and makes their lives easier.

Before:

• yarn build compiled the assets from ALL packages, it was not possible to build packages from only one package (which is useful if you work on a single package)
• no yarn watch
• yarn test runned tests from ALL packages, like yarn build, it was not possible to run tests for only one package

Now:

• at the project root, build/test/lint/format/check-lint/check-format scripts will run on all assets from all packages. And it will be faster than before, when processing was sequential, but now it's parallelized.
• at a package root (ex: src/Map/assets), build/test/lint/format/check-lint/check-format scripts will run on all assets from this package only
• build and watch scripts handles both TypeScript and CSS files in a single command

This is a first step to what we spoke about with @smnandre to write a contribution guide.
It is now much more easier and friendlier to tell a developer to run yarn watch inside a package root, instead of telling it to run ./node_modules/.bin/rollup -c --environment INPUT_FILE:src/Map/src/Bridge/Google/assets/src/map_controller.ts -w (and more, if you have multiple files).

[smnandre]

This is so grea! And it does run very quickly!

Congrats and thank you 🙇