Add baseline builtins for CreateAsyncFromSyncIterator and
GetImportMetaObject, and call those instead of the runtime functions.

Drive-by remove some TODOs in baseline-compiler.cc which are either no
longer planned or don't need to be done any time soon.

Bug: v8:11420, v8:11429
Change-Id: I15b4fe1f04316492045250b2c65ab6016f29b313
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2699261
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72808}