This isn't remotely ready for primetime, but it does prove out the
basic viability of @chadhietala's suggestion that we may not need to
fix all the circularities before we can publish. We in fact can just
publish as is: none of the circularities are *hard* blockers, at least
for *this* part of the effort (though they will be for getting docs
published with these as the source of truth).

The things we will need to do to be able to execute the rest of the way
on this, given our goals:

- Fix a couple cases where we are using private names in public types,
  specifically around the `OWNER` from `@glimmer/owner`.

- Put the hacky `generate-tsconfigs.mjs` script somewhere besides the
  root, expand its capabilities to include wrapping generated modules
  in a `declare module` statement and running Prettier on the result,
  and rename it accordingly.

- Land @wagenet's in-progress PR (#20175) to convert the `ember`
  package to TS so we can publish types for it, which will unblock some
  of the other Ember packages as well.

- Properly exclude the parts of Ember's APIs we *don't* want to be
  publishing (all the purely-internal and private stuff).

This lets each config specify *only* how it actually does a build (or
not!), while sharing the config explicitly.

There are pre-existing runtime shenanigans in `@ember/object/internals`
to add debug-only errors to the class in dev builds. Those runtime
shenanigans produce the need for type-level shenanigans to match: TS
gets stuck here because the runtime shenanigans declare
`FrameworkObject` with a class expression (rather than the usual class
declaration form). That in turn means TS needs to be able to fully name
the type produced by the clsas expression, which includes the `OWNER`
symbol from `@glimmer/owner`.

By explicitly giving the declaration a type when assigning it the class
expression, instead of relying on inference, TS no longer needs to name
the `OWNER` property key from the super class, eliminating the private
name shenanigans.

Co-authored-by: Dan Freeman <dfreeman@salsify.com>

- Add `.gitattributes` so GH will syntax highlight it correctly.
- Improve the naming, so: `tsconfig/compiler-options.json` etc.