This implements complete support for multisample array textures on the
D3D11 backend. There's a specialized TextureD3D class as well as a
TextureStorage11 class for multisample array textures that have the
bulk of the functionality.

BUG=angleproject:2775
TEST=angle_end2end_tests, angle_deqp_gles31_tests

Change-Id: I68116635c01cef0e48c089fd9da05a844ef2d802
Reviewed-on: https://chromium-review.googlesource.com/1216003Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>