Add a CacheStats class that provides cache hit and miss bookkeeping.
All internal caches make use of this class to keep track of its stats.
This provides a means to profile cache hit ratios a.k.a Vulkan object
reuse for any application.

Bug: angleproject:5447
Test: Manual verification with angle_end2end_tests
Change-Id: I44eeb0c2b9b291ec1cdd156fb2be4a5fe80d2848
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2580111
Commit-Queue: Mohan Maiya <m.maiya@samsung.com>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>