(optim/fix): only emit type declarations once

[agilgur5]

• every other emission is just a duplicate -- no need to spend compute
  time to make duplicates

  • even for the upcoming multi-entry, the same types are emitted for
    each entry as the compiler just emits types for everything in the
    tsconfig include

• fixes a long-standing bug with the deprecated moveTypes() function
  that would occasionally cause types to not be properly output

  • this was actually due to moveTypes() being run multiple times in
    parallel (as well as the types themselves being emitted multiple
    times in parallel)
    • hence the EEXIST and ENOENT filesystem errors being thrown, as
      that directory was being changed multiple times in parallel
      • race conditions, fun!
  • now they're only emitted once and only moved once, so no problems!

• also fixes a bug with an initial version of multi-entry where if an
  entry in a subdir of src/ were added, e.g. src/foo/bar, the entire
  tree of type declarations would get output into dist/foo/src/*.d.ts

  • alternatively, could call moveTypes() with an arg for each entry,
    but there's no need since all declarations get produced the first
    time around anyway
  • similar bug occurred with an initial version of --preserveModules
    that used separate format directories

Also threw in another TS optimization here with the cacheRoot change that's along the same lines but slightly different of a change.

---

This is extracted out of #367 's 14b5397, but is a better version in a few ways:

1. Doesn't have issues with declarationMaps as they've also been set to false. Otherwise would get errors / test failures that you can't have declarationMaps without declarations
   • Better testing around this nowadays revealed this bug
2. : undefined still overrode some declaration/declarationMap settings, also causing errors / test failures, so changed this to not set either on the first emission
3. moveTypes() was moved into a then of the asyncro() so that it's still part of the progress estimation.

The bugs this fixed in #367 and by extension #535 should no longer be present anyway since #367 switched/improved to use Rollup's code-splitting instead of a separate build & bundle per entry and #535 will need to be updated to use the same output.entryFileNames as a later version of #367 used instead of using separate format dirs.

---

I also realized that this might fix the bugs with moveTypes() that gave us so many CI issues prior to #504 very recently in #500 (comment).
And indeed this does fix those bugs, hence the removals of the error throwaways and a change in the deprecation message by a bit (it's still a problematic option, with another caveat other than those listed that moveTypes() doesn't apply to custom declarationDirs, though that could be fixed). I tested that this was the case by changing rootDir to ./ in every test fixture and running tests a couple of times and no errors were thrown anymore!

---

The cacheRoot optimization is also related to #328 / #329. And might make #618 obsolete.

[agilgur5]

Ah, also should note that from my local test runs, the time it took to run all tests decreased by 10-15%, which is a substantial perf improvement!
If this tiny change was so substantial, switching to per-ouput plugins is really going to be big when building multiple output formats 😮

[agilgur5]

LGTM. straightforward, small diff, and already went through a few iterations.