Vulkan: Support VS, FS, and CS in the same PPO This CL adds support for a Program Pipeline Object to have a VS, FS, and CS attached to the same PPO and then using that PPO for both draw and dispatch calls. Bug: angleproject:3570 Test: KHR-GLES31.core.compute_shader.sso* Change-Id: I262cdbdfd442f6db5ba2b45d1308003102b237cb Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2150078 Reviewed-by: Tim Van Patten <timvp@google.com> Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com> Commit-Queue: Tim Van Patten <timvp@google.com>