When a sampler's GL_TEXTURE_SRGB_DECODE_EXT state
was toggled between GL_DECODE_EXT and GL_SKIP_DECODE_EXT
VkImageViews of the TextureVk object were not being updated.
Add sRGB_decode state as part of ImageViewSubresourceSerial
so we retrieve the correct VkImageView from the texture cache.

Bug: angleproject:3609
Tests: angle_end2end_tests
       --gtest_filter=SRGBTextureTestES3.SRGBDecodeSamplerParameterToggle*Vulkan
Change-Id: I897e461957d408b5a5b4f03fefc05f2e9684c7b7
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2514900
Commit-Queue: Mohan Maiya <m.maiya@samsung.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>