This patch refactors how DXGI format info is stored. The goal is to
make it easier to make changes that affect both swizzle formats and
regular texture formats, and make it easier to pass the format sets
around.

BUG=angleproject:1244
TEST=angle_end2end_tests

Change-Id: I1cc220bccbbdde9200a41829fdc37c8ec123c6a1
Reviewed-on: https://chromium-review.googlesource.com/329072Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>