This moves a lot of the code in VertexArrayVk into ContextVk. Having
the code in a centralized place makes the code a bit more organized
since the Context is reponsible for binding state to the command
buffers. It also makes it easier to use dirty bits to track the command
buffer state.

Bug: angleproject:2786
Change-Id: I5cefbb14028e8f3fe651f26e997ca88f8f1c7628
Reviewed-on: https://chromium-review.googlesource.com/1188953
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>