Vulkan: Remove ProgramExecutableVk back-pointers. This removes the mProgram and mProgramPipeline back-pointers from ProgramExecutableVk. In order to fix this, we needed to refactor the VkPipeline init functions to call through ProgramExecutableVk only instead of passing through ProgramVk. We also needed to move the early fragment shader optimization boolean out from Program. This CL also fixes a few places where the early fragment test optimization boolean wasn't properly updated. Bug: angleproject:3570 Change-Id: Ie4c48087f6eb022e6f0a4dacc2710085165d49e1 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3408267 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Tim Van Patten <timvp@google.com> Commit-Queue: Jamie Madill <jmadill@chromium.org>