Vulkan: Zero-init ContextVk dirty bit handlers.
Vulkan: Zero-init ContextVk dirty bit handlers.

This allows for a better debugging experience and can solve some
potential invalid ASSERTs due to some dirty bit handlers not being
initialized.

Bug: angleproject:4622
Change-Id: Ib34e35dea6c6c7de250ae6600576f0324c150ae6
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2233403
Commit-Queue: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Reviewed-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>

ppy/angle,ppy/angle,ppy/angle,ppy/angle