Includes changes from jmadill to align with Vulkan backend design.

Correctly setting layer count and depth when the texture type is
2Darray. Vulkan requires depth of 1 for 2Darray textures.

Bug: angleproject:3189
Change-Id: I0d58c33fcd75b1d768ea0308ac6e54230d8cfcc5
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1721169Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Commit-Queue: Cody Northrop <cnorthrop@google.com>