It is not legal for destructuring patterns and identifiers in declarations
to be in parentheses. This includes nested patterns/identifiers inside
another pattern.

We were checking sub-patterns for parentheses when parsing possible
sub-patterns, but this check missed sub-patterns with a default
initialiser (e.g. [({x:y})=1] = {}), as the AssignmentExpression hid
the pattern.

So, we now additionally record declaration/pattern errors of an assignment
LHS when parsing the assignment cover grammar.

Bug: v8:8630
Change-Id: Ia5a97003671fc1da7f68d7fb15943928ce9496e3
Reviewed-on: https://chromium-review.googlesource.com/c/1404452Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58743}