The grammar in GLSL ES 3.10 does not impose a strict order on the
qualifiers and also allows multiple layout qualifiers.

This patch relaxes the checks when parsing a type qualifier.

BUG=angleproject:1442

TEST=angle_unittests

Change-Id: Ib3653a1ed1bfced099a6b2cbf35a7cd480c9100a
Reviewed-on: https://chromium-review.googlesource.com/379016
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>