Vulkan: Pass RendererVk to Allocate helpers. Passing the Renderer pointer instead of the Context pointer makes these methods a bit easier to work with from the "EGL" sections of the code. This is a refactoring-only change to aid the Depth/Stencil implementation. Bug: angleproject:2357 Change-Id: Icbcc72a1daff4edd947a21672744498781cfc064 Reviewed-on: https://chromium-review.googlesource.com/919523 Reviewed-by: Luc Ferron <lucferron@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>