- Mark arrow functions the uncommon assignment case
- arrow formal parameter productions are ignored by default already
- avoid duplicate is_destructuring_assignment branch
- immediately pass expected productions into Accumulate

Change-Id: Ifaeece53a1d6b99999ea298518702e82bc20db73
Reviewed-on: https://chromium-review.googlesource.com/c/1326941
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57364}