Vulkan: Make vk::FramebufferHelper the graph resource. It seems conceptually easier to understand that a vk::Framebuffer is the resource used in graph. Rather than making the GraphResource be integrated into the FramebufferVk class itself. This means that the only objects that are graph resources are Vulkan objects: Images, Buffers, and Framebuffers. Refactoring change only. Bug: angleproject:2828 Change-Id: I59d60643182287d4b1fcf9730a3c3a0da5b65973 Reviewed-on: https://chromium-review.googlesource.com/1249561 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Frank Henigman <fjhenigman@chromium.org>