Vulkan: Selectively dirty DIRTY_BIT_SAMPLE_SHADING When program executable changes dirty DIRTY_BIT_SAMPLE_SHADING bit if either the current or previous program enabled per sample shading Bug: angleproject:386749841 Change-Id: I82aa7df29473e455aa68dfba9fefdb1bc712a78d Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6622156 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>