Variable locations and descriptor set/binding values are calculated
multiple times:
- Compiling GLSL->SPIR-V
- Creating the Vulkan pipeline layout
- Updating descriptor sets

These values should instead be calculated once and reused throughout
since they won't change without recompiling the shader program.

Bug: angleproject:3570
Change-Id: I5d8767b3b2e2f741aade7fec9991eea53ee2eb98
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2067101
Commit-Queue: Tim Van Patten <timvp@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>