Parenthesized variable names are valid references for assignment. To make sure
we can properly mark the variable as assigned, we should push parenthesized
variables to the outer expression scope after the parenthesized expression is
guaranteed to not be an arrow head; so that the variable list of the parent is
complete.

Technically we could probably get by with simply pushing a single variable,
since more complex expressions aren't valid parenthesized assignment targets:
(a) = ... and [(a),(b)] = ... are valid, but ([a,b]) = ... isn't.
It doesn't really seem worth it though.

Bug: chromium:1015372
Change-Id: I095c35126742a14d0171537b9795f7258c33ab4d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1872389
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64455}