Use array_specifier in struct declarator parsing This will make implementing arrays of arrays simpler for struct members as well. Similar refactoring was already done for other types of array declarations. BUG=angleproject:2125 TEST=angle_unittests Change-Id: I0483c3a7c006d37090c7c972cb3d7763d3909c8f Reviewed-on: https://chromium-review.googlesource.com/739824 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Commit-Queue: Corentin Wallez <cwallez@chromium.org>