This adds support in blit11::copyTexture for LUMA, LUMA_ALPHA, and ALPHA
formats as destinations. Added is handling for each case to match up
the corresponding shader. This required new premultiply and
unmultiply D3D11 shaders for some cases.

Changed copyTextureCHROMIUM validation to allow new formats.

Tests have been created to demonstrate using copyTextureCHROMIUM with
the new formats with default parameters, as well as with the
unpackPremultiply and unpackUnmultiply parameters.

BUG=:angleproject:2101

Change-Id: Id8cd303a46fe70710bc18172fc938552a6e4cfaf