Allow typescript transforms via Compiler API

[jimsimon]

I'm interested in writing a typescript transform that rewrites all of the Import declarations to named identifiers and outputs an import map. The idea being that this could be the basis for a frontend dependency management tool that could handle semver resolution and deduping transitive dependencies. As far as I can tell there's no way to pass transforms via the Compiler API. Adding the ability to do so could potentially open up a wide range of output customizations.

Alternatively I could write a tool that does that before deno is called, but I'd prefer the above approach because aking multiple passes at the source code would be slower than making a single pass

[bartlomieju]

Duplicate of #3354