Use active textures mask in GL and Vulkan. This also inlines a few accessors and changes the type of the texture cache. Bug: angleproject:2763 Change-Id: I82f3c508613f6284d835e8cb64808cfe26a56161 Reviewed-on: https://chromium-review.googlesource.com/1166142 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>