The smart merge feature has been dropped from the webpack-merge library
that we were using. Use the basic merge feature instead since we're not
actually doing anything too complicated.
Also don't return null from the WorkerConfig as it can't be correctly
merged.
This PR implements much of the static assets rework ADR [1], including:
* `npm run build[-dev]`, and its subcommands,
* `npm run webpack[-dev]` and
* `npm run compile-sass[-dev]`.
This is backwards-compatible. `paver update_assets` should not be affected.
The new command warns that it is "experimental" for a few reasons:
* `npm run build` will fail in the webpack phase unless you first
run `xmodule_assets`. This will be changed soon [2].
* We have tested the new build, but not quite so thoroughly that we'd
recommend it as the production default yet. Once the xmodule_assets
work lands, we'll share this on the forums so early adopters can try it
out.
* The commands lack some top-level documentation. Once they stabilize more,
we'll add a section to the README that explains how and when to use `npm run
build` and its subcommands and its env vars.
* `npm run watch` is not yet implemented.
References:
1. https://github.com/openedx/edx-platform/blob/master/docs/decisions/0017-reimplement-asset-processing.rst
2. https://github.com/openedx/edx-platform/pull/32685
Part of: https://github.com/openedx/edx-platform/issues/31604
