Implements support for the glBlitFramebuffer edge case in the
EXT_sRGB_write_control spec, and fully exposes this extension.

Bug: angleproject:5075
Test: SRGBFramebufferTest*.*Vulkan*
Change-Id: I05f044abbc5cb272825d1fc4b9028217f18e63c2
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2785641Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Mohan Maiya <m.maiya@samsung.com>