dEQP assumes there are more than one atomic counter buffers available.
This is technically not a requirement by the standard, but nevertheless
could be what applications expect as well.

This change adds support for multiple atomic counter buffer bindings.
This is done by declaring an array of storage buffers for the atomic
counter buffers (instead of declaring only one) and passing the
(binding, offset) pair around to functions instead of just the offset.
The atomic counter is found by indexing `binding` into the storage
buffer array first before indexing `offset` into its `uint[]`.

ProgramVk's default uniform collection is also fixed not to include
atomic counter uniforms.

A remaining issue is that atomic counter buffer offsets don't have
alignment requirements in GLES, but Vulkan does for storage buffers.
Similar to emulated transform feedback buffer offsets, these should be
sent to the shader through uniform values.  This will be done in a
follow up change.

Bug: angleproject:3566
Change-Id: I5600225c24c38f1a8ecf5c64388073055733197d
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1707931
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>