Use rules_jvm_external for internal dependencies

[jadenPete]

Description

This PR is the second in a series to refactor the ruleset to use rules_jvm_external for fetching all Maven artifacts.

It deletes scala/private/extensions/dev_deps.bzl and refactors the ruleset to pull all internal dependencies (previously declared in that module) using rules_jvm_external. It also makes rules_jvm_external a required dependency of the ruleset.

Motivation

Please see this PR for more information on this initiative and the motivations behind it:
#1775

[mbland]

Quick comments:

• Please use the typical Description and Motivation pull request template, even for these smaller PRs.
• This appears to have broken 'test_twitter_scrooge_example' from 'test/shell/test_examples.sh'. Does test/shell/test_examples.sh (as well as ./test_run.sh) fully pass locally?
• Please break out the buildifier-prebuilt into its own pull request. That seems worth landing independently of the rest of this change.

I think I'm beginning to see some of the benefit of using rules_jvm_external here. I have a few comments to make, but I'll return to this after the buildifier-prebuilt change lands and this pull request fixes the test_twitter_scrooge_example breakage.

Note that if/when #1785 lands, which should happen first (if we decide to merge it), both the buildifier-prebuilt change and this PR will require rebasing and making MODULE.bazel.lock updates.

[jadenPete]

Thank you for the comments! My bad, I've updated the description to follow that format.

Working on splitting out the buildifier-prebuilt changes and fixing the failing test now.

[jadenPete]

Ok, I've opened a separate PR for the buildifier_prebuilt changes!
#1788

Also, the tests should pass now. That PR needs to be merged before this one, so consider this PR to be stacked on that one and please ignore the first commit when reviewing it.