Make "isCompute" private to ProgramExecutable. This eliminates uses of "isCompute" is the Vulkan back-end. Instead of checking the state flag, we can use the context of the current command to determine if we're running a compute or a graphics command. This will eventually lead to us being able to compile the program pipeline objects before we run a draw or dispatch command. Changes the driver uniforms descriptor desc to bind to both graphics and compute shader stages to simplify the code. This could have theoretical but low-risk performance implications. Bug: angleproject:6595 Change-Id: Ie30d419b6ece5b33f5066a034d3805fe96519b36 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3233903 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Tim Van Patten <timvp@google.com> Commit-Queue: Jamie Madill <jmadill@chromium.org>