Move load functions table to renderer layer. We will be able to use it for the Vulkan formats table. BUG=angleproject:1455 Change-Id: Iddc09fe560b06880af72a6fa8eb03fa2792e2f8c Reviewed-on: https://chromium-review.googlesource.com/367454 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>