The copied data is not supposed to have sRGB conversions applied to it
when written to the destination texture but an sRGB SRV is used by Blit11.
Instead of creating multiple sRGB and non-sRGB SRVs for textures, simply
fall back to the CPU copy path for this format for now.

Clip color channels that should not exist in the destination texture
formats in Image11::CopyImage.  This works around issues with texture
formats with emulated channels.

TEST=conformance2/textures/image_bitmap_from_canvas/tex-2d-srgb8-rgb-unsigned_byte
TEST=conformance2/textures/image_bitmap_from_canvas/tex-2d-srgb8_alpha8-rgba-unsigned_byte

BUG=angleproject:1932

Change-Id: Ieeda3569f80d016fda781e7eb498acd3b97568d0
Reviewed-on: https://chromium-review.googlesource.com/559857Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>