WIP: Become our own blueprint

[NullVoxPopuli]

On hold: going to try patching TypeScript support in to the blueprint how everything else is layered on top today.

Maybe it won't be so bad

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Goals:

• inline the upstream blueprint so we no longer need to rely on it
• enable (in a future PR) fixing TypeScript support
• enable (in a future PR) correct default linting (for both gjs and gts)
• enable (in a future PR) correct default formatting (for both gjs and gts)

Todo:

• copy over a bunch of tests from ember-cli, and update them accordingly
• ensure that, for JS / GJS, tests can run, lints can run etc (ensuring retention of pre-existing support for this blueprint)