Implements a descriptor set cache for UBOs, SSBOs, and atomic counter
buffers. Storage Images and framebuffer fetch input attachments are
not yet included. Requires moving the buffer barrier handling into
ContextVk, similarly to how we handle the barriers for Textures.

The packed description key for the descriptors uses a "fast" vector
with a basic minimum size. For most cases of a few buffers this will
fit easily in stack memory, but for larger programs with many buffers
we fit this into heap memory. The key has a large upper bound due to
the high ES 3.2 requirements and the need to index several values such
as the offset and binding size.

We use dynamic offsets for uniform buffers when possible. This ensures
applications like Manhattan 3.1 that use sets of common buffers with
changing offsets hit the cache most of the time.

Because of resource limits we pick at compilation time whether to use
dynamic or static descriptor sets. Mostly this applies to tests that
use a large number of uniform buffers. A future implementation could
be smart and would recompile the program with heuristics to use a
minimal number of dynamic indices.

Reduces the number of descriptor set updates from ~300 -> ~30 per frame
in Manhattan 3.1 and in Asphalt 9 from 900+ to as low as 0 per frame.

Bug: angleproject:5736
Change-Id: I5c2a3881bec90d301dab15cc86c8a70e60674ad7
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2757515
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>