This switches the tracking for the uniform, shader storage, and atomic
counter buffers to use bitset masks to determine where there are
active buffers. This will make iterating these buffer sets faster.

Also renames the limit for atomic counter buffers to be consistent
with the other buffer types.

Also applies the implementation limit to atomic counter buffer
bindings. This fixes out-of-bounds access on some Linux platforms that
expose a large number of bindings.

Bug: angleproject:5736
Change-Id: Ice801645697592d1dda6aebf0cb69767594cc0c5
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2757509
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>