Provide workarounds for both TS (bad peer-provided types handling) and Glint (mishandling of extensions) issues

[NullVoxPopuli]

This isn't ideal, and I would have PR'd it sooner, but I was kind of hoping that we'd have solutions to these problems by now... but we don't.

To unblock people and to make the blueprint usable for folks wishing to use typescript, we need this work around.

Here are the issues that this PR resolves:

• https://github.com/microsoft/TypeScript/issues/56571#issuecomment-1830436576
• https://github.com/typed-ember/glint/issues/628
• https://github.com/typed-ember/glint/issues/697