Try using Bazel Modules to clean up WORKSPACE files

[alexjpwalker]

Now that we're upgrading our repos to use Bazel 6, we have access to the powerful new Bazel Modules feature, which is supposed to be able to make the declaration of dependencies in WORKSPACE files, etc. sharply cleaner and more bulletproof.

• https://bazel.build/external/module

We should investigate, and try using them ASAP. I'm hoping we'll be able to make our WORKSPACE files more maintainable and easy to work with.