Since [RFC 0748][0748], Glimmer components support a `Signature` type
which specifies any arguments they accept, any blocks they yield, and
the element types to which `...attributes` are applied. Incorporate the
signature when generating TS blueprints for Glimmer components,
including template-only components. Do *not* generate them for Ember
(classic) components, since there are severe limitations in using
classic components that way, and since we only support the Octane
programming model in our TypeScript support per [RFC 0800][0800].

[0748]: https://rfcs.emberjs.com/id/https://rfcs.emberjs.com/id/0748-glimmer-component-signature/
[0800]: https://rfcs.emberjs.com/id/https://rfcs.emberjs.com/id/0800-ts-adoption-plan/

For the fallback case, where Ember's blueprints are being executed by a
version of Ember CLI earlier than 4.3.0, the emitted blueprints *must
not* include any TypeScript types, since the CLI will not be able to
remove the types. Accordingly:

1.  Return a boolean flag from the `maybePolyfillTypeScriptBlueprints`
    helper, indicating whether the blueprint is in a mode where it can
    reliably *emit* types.

2.  Use that new helper in the component blueprint so that it can avoid
    emitting a signature type, and specifically can avoid emitting it
    as a type parameter on the class or function default export.