Implements the `npm run watch` section of the assets ADR [1], plus some
modifications since I decided to switch from pywatchman to watchdog (see
ADR changes for justification). This will replace `paver watch_assets`
(edx-platform) and `openedx-assets watch-themes` (Tutor).
Specifically, this PR adds three experimental commands:
* `npm run watch-sass` : Watch for Sass changes with watchdog.
* `npm run watch-webpack` : Invoke Webpack-watch for JS changes.
* `npm run watch` : Invoke both `watch-sass` and `watch-webpack` simultaneously.
These commands are only intended to work in development mode. They have
been tested both on bare-metal edx-platform and through `tutor dev run`
on on Linux.
Before removing the "experimental" label, we need to:
* Test through Devstack on Linux.
* Test through Devstack and `tutor dev run` on macOS.
* Test on bare-metal macOS. Might not work, which is OK, but we should
document that.
* Document the commands in edx-platform's README.
* Confirm that this not only works through `tutor dev run`, but also as
a suitable replacement in the `watchthemes` service that Tutor runs
automatically as part of `tutor dev start`. Tweak if necessary.
References:
1. https://github.com/openedx/edx-platform/blob/master/docs/decisions/0017-reimplement-asset-processing.rst
Part of: https://github.com/openedx/edx-platform/issues/31612
303bf5ef3c
