TypeScript conversion so we have accurately generated types for consumers

[NullVoxPopuli]

These 3 PRs should be merged first:

• Prevent CI from running twice on PRs #276
• We don't need to test against different node versions as we have no build behavior #277
• Pull forward the lint changes from #275 #278

As ember has first-class TypeScript support out of the box (almost), we need to to have all core addons also support that.

Like always, consumers don't need to use TypeScript, but our library code using TypeScript will provide better intellisense for both JavaScript and TypeScript users.

Incidentally, achieving more alignment with the TS-v2-addon blueprint, we gain support for Glint-using projects.

This work continues the work of #246

Demo in the docs app:

Changes:

• convert to TS
• npx ember-apply typescript to the docs app
• set up Glint in the docs app
• test with Glint in the docs app
• upgrade the test-app to latest ember-source -- (fastboot + embroider) is not bug free with ember-source 3.28, but is with latest ember-source. Going to inquire with the embroider folks if this combo should be supported. It could also be that the 3.28 folks need to use an earlier version of embroider -- idk how complex / thorough we want the test matrix to be

[NullVoxPopuli]

Current issue with the embroider tests.

what in tarnation is going on. broccoli doesn't go in the browser.

[NullVoxPopuli]

this is a template-only component, and thus has no this

[wagenet]

I didn't verify every single line, but the overall direction looks correct to me.