Use the Vulkan format table to look up the Vulkan format for vertex data.
This will let us support more vertex formats by adding them to the table.
It also eliminates one usage of gl::VertexFormatType.
No functional change.

BUG=angleproject:2405
BUG=angleproject:2531

Change-Id: I73eb69ccac50d427de3e7d5479f92bb17c49aed3
Reviewed-on: https://chromium-review.googlesource.com/1051028Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Luc Ferron <lucferron@chromium.org>
Commit-Queue: Frank Henigman <fjhenigman@chromium.org>