Remove checks that would never fail, and refactor the functions into
more self-contained checks. For example, it doesn't make sense to
check the qualifier from the part of the type that doesn't contain the
qualifier.

This prepares for adding the parsing of arrays of arrays.

BUG=angleproject:2125
TEST=angle_unittests

Change-Id: I1144bee35d2b04c7cb22e2bb7e17307298e35f8c
Reviewed-on: https://chromium-review.googlesource.com/629016Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>