Implemented support for EXT_texture_format_sRGB_override
This is done by creating new imageviews for textures with sRGB
overridden that reinterpret the format to its sRGB counterpart.
As preparation for this, textures that use this feature are
reallocated with VK_IMAGE_CREATE_MUTABLE_FORMAT_BIT. This will
have a performance cost for textures that use this feature, but
should have no performance cost for regular textures, since they
will not have this bit set.

Bug: angleproject:4561
Test: angle_end2end_tests --gtest_filter=SRGBTextureTest.*Vulkan*
Change-Id: Iba25f1f2b0a7227959c1cb4ba6e3ca8311c20d06
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2152145
Commit-Queue: Mohan Maiya <m.maiya@samsung.com>
Reviewed-by: Tim Van Patten <timvp@google.com>