Rather check expressions used as patterns directly. Check parentheses by
tagging parenthesized expressions as parenthesized.

This allows us to drop UnexpectedPatternToken and makes it clear why a specific
token is unexpected (because it's invalid in a binding pattern).

This also more uniformly restores messages like "Invalid destructuring
assignment target".

Change-Id: Idd98e9116c85de4c2304cf1fef1baa097b67149d
Reviewed-on: https://chromium-review.googlesource.com/c/1349572
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57792}