The configuration used to build our JavaScript (Rollup, TypeScript,

Babel configuration, and browser compatibility list) are now provided as

part of the Review Board package. This enables us to refer to these

configuration files in future extensions, helping extension authors

maintain modern JavaScript codebases and leveraging any improvements or

compatibility changes we make.
We do specialize some of this for building Review Board itself, but the

vast majority is now common configuration.
As part of this, we now set up a .npm-workspaces directory containing

symlinks to the Djblets and Review Board static roots.
For Djblets, this replaces the old .djblets symlink that lets us use

our in-development modules of Djblets easily.
For Review Board, this just points to our in-tree code.
We could instead use rollup-alias to give us this same capability, but

since we're already setting this up for Djblets, it makes sense to stay

consistent.
Note that after this change, setup.py develop must be re-run.

Successfully built the Review Board package.
Verified the new files were included in the package and source

distribution.
Tested accessing the website with freshly-compiled static media.