Vulkan: Reorganize helper classes. This renames ResourceVk to vk::CommandGraphResource, which should help clarify its usage. This also moves LineLoopHandler, ImageHelper, and the DynamicBuffer and DynamicCommandPool classes into a new vk_helpers module. This file contains helper classes that manage other resources. Also this makes DynamicBuffer and DynamicDescriptorPool no longer inherit from CommandGraphResource. In the future, only Impl objects will be allowed to be graph resources. Bug: angleproject:2318 Change-Id: I0fa23da2ac853d90f3c822547a4a314f247cc757 Reviewed-on: https://chromium-review.googlesource.com/985200 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Frank Henigman <fjhenigman@chromium.org>