This change makes a bunch of changes to modernize our JavaScript build

process across our products:

Support npm workspaces
In order to better support development across our many repos and

packages, this dramatically improves the way we handle npm workspaces.
We used to have a djblets/package.json file which defines our JavaScript

dependencies, and then a symbolic link from the repo root to make that

also available for npm install. This change removes the symbolic link,

and adds a new top-level package.json which defines workspaces as

djblets and .npm-workspaces/*. This allows creating symbolic links

in the workspaces directory in order to bring in development copies of

spina, ink, beanbag-eslint-plugin, or whatever other JS dependencies one

desires.
Depending on the package, this may require having a shared parent

directory and a symbolic link from ../node_modules to

./node_modules, since some things like to resolve to absolute paths

and then crawl up the directory tree (looking at you, tsc).

Update and consolidate JS dependencies.
The actual dependencies listed in djblets/package.json have been

simplified, using the new @beanbag/js-buildkit metapackage to ensure

build-time dependencies. We also no longer have an explicit dependency

on spina and backbone versions, preferring instead to just inherit

whichever versions we're getting from ink.

Use modern invocation for static media builder utilities.
We were hard-coding the locations for babel, lessc, rollup, and

uglifyjs based on node_modules/.bin. Because of the vagaries of npm

we can't necessarily assume that there's a node_modules in the current

directory, or that things will be in .bin. I've changed these to use

npm exec ... instead, allowing npm to locate the binary and invoke it.

Use terser instead of uglifyjs (opt-in).
UglifyJS lacks support for a lot of ES6+ features, and its cousin

UglifyES is unmaintained. I've changed our pipeline configuration to use

Terser instead, which is a fork of these which is actively maintained

and supports newer JS. The actual dependency for this will live in

@beanbag/frontend-buildkit.
Some of our upstream dependencies already depend on terser, so this

reduces our dependency footprint as well.
I was hoping we would be able to get sourcemaps for the fully-compressed

JS with this, but unfortunately the way that django-pipeline does

compressors won't allow for that.

Use modern pipeline setup for static media during tests.
Unit tests had their own pipeline configuration for some reason, which

didn't even include any of the rollup files. This has been replaced with

a call to the same build_pipeline_settings that we use everywhere

else.

Pulled in backbone types.
I'm working on upstreaming our changes and improvements to the type

definitions for Backbone, but in the meantime we can't just reference

the file from node_modules the way we did before. This has been copied

into the Djblets tree for the time being.

Updated to ESLint 9.
With the newer @beanbag/eslint-plugin bundled in

@beanbag/js-buildkit, we now use ESLint 9.

Simplify browserslist.
I've changed the browserslist config to exist inside the top-level

package.json and just specify baseline widely available. This mirrors

what we have in Review Board (though RB also has that in our shareable

babel config).

Set up Djblets into an environment that used npm workspaces to include

  Djblets, Review Board, @beanbag/frontend-buildkit, @beanbag/js-buildkit,

  @beanbag/jasmine-suites, and @beanbag/eslint-plugin.
Ran unit tests.
Ran eslint.
Built static media.
Built the rbintegrations extension to verify that static media

  building still worked for that.