Keep parsing the rest of the MemberExpression after `new.target`

BUG=v8:6745
R=marja@chromium.org, adamk@chromium.org

Change-Id: I53cc370766e72ed9e36c5c7aa150a3ad9a6062f8
Reviewed-on: https://chromium-review.googlesource.com/627756Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Caitlin Potter <caitp@igalia.com>
Cr-Commit-Position: refs/heads/master@{#47615}