Add FastIntegerSet container to enable fast contains operation
for a set of integer keys. The class uses a BitSet vector to
achieve performance.

Add FastIntegerMap container to improve buffer serial
tracking performance. FastIntegerMap uses FastIntegerSet container
to track buffer serial keys. It also provides an ensureCapacity
method to reserve space, for the expected buffer count, upfront.

CommandBufferHelper::mUsedBuffers and ContextVk::descriptorSetCache
are now FastIntegerMap
CommandBufferHelper::mRenderPassUsedImages is now a FastIntegerSet

Based on a CL by Jamie

Bug: angleproject:4950
Test: angle_unittests.exe --gtest_filter=FastInteger*
Change-Id: Ib58be20143f588baab99acadac796f2435f72d54
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2369466Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Mohan Maiya <m.maiya@samsung.com>