Better monorepo support. Use @embroider/addon-blueprint

[NullVoxPopuli]

tl;dr: this becomes a serious project 🙃

Lots of quality-of-life improvements in here, but some tradeoffs that will be less trade-offy as upstream things get resolved.

Support for npm, yarn, and pnpm workspaces, given: embroider-build/addon-blueprint#36

JS Support

• js support is now much better, because I'm using the v2 addon blueprint (with all the flags that have been added for configuring package paths), and modifying the output of that (whereas previously I was building a v2 addon manually)

TS Support

• ts support is now worse in the migrator, because I'm waiting on --typescript in @embroider/addon-blueprint and the ember-cli app blueprint
• will be powered by: Add Typescript support embroider-build/addon-blueprint#42

TODO:

• Support Phased migration
  • Phase 1: move the tests to their own app
  • Phase 2: convert the addon to v2
• Support downgrading dependencies from the v2 blueprint (rollup-plugin-ts @v2) -- maybe

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Latest commit: a7e148b

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[NullVoxPopuli]

Gonna merge since this PR has gotten ridiculous, C.I., and the aforementioned features can be developed in PRs that are actually easy to review.