Idea: Distinguish between build-signature declarations and for-publication declarations

Some declaration files are intended for publication and they need to be readable and "work" (e.g. no imports from node_modules). Others are, from a user's perspective, basically temporary files produced by the build to make subsequent builds more incremental (i.e. faster). Right now, we produce both sets of declaration files in the same way, but maybe we don't need to? As far as I can tell, the characteristics we require from "build" declarations are:

1. They change if-and-only-if the API of the underlying code changes
2. A source map can get you back from the declaration file to the input file

We can satisfy these requirements without, e.g.

1. Pretty-printing
2. Adding imports (as in #44044)
3. Confirming that referenced types are actually accessible (simplifying #44045)
4. Complaining about node_modules imports

One likely snag is how users will opt in to this behavior (Is it enough to be composite/incremental without having declarations? Is yet another switch required?).

Start by reading the issue's distinction between build-signature and publication declarations, then investigate the existing composite/incremental and declarations behavior. Review the related discussions in #44044 and #44045. Done would require a decided opt-in design and implementation that preserves API-change tracking and source-map navigation while relaxing publication-only checks for build declarations.