This is groundwork for some upcoming changes where data from
ContextVk is needed in GraphicsPipelineDesc::initializePipeline().
Passing ContextVk ptr all the way down instead of the reduced
vk::Context ptr.

Bug: angleproject:2672
Change-Id: I29f580c3503777085355f1b79f4ae4552a394557
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1811433Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>
Commit-Queue: Tobin Ehlis <tobine@google.com>