Using VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT in pWaitDstStageMask doesn't
create a dependency, since no memory is accessed during that stage.
Switch to VK_PIPELINE_STAGE_ALL_COMMANDS_BIT to synchronize all accesses.

This fixes flickering observed in WebGL on ARM GPUs when composited using
Vulkan in Chromium.

Bug: angleproject:4422
Change-Id: I37da461c03dbf52f8658408b159c2b173cccd0b3
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2068906Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Michael Spang <spang@chromium.org>