Vulkan: Keep the output variable of TCS active for barrier OpControlBarrier implicitly synchronizes 'Output' storage class. If TCS has an out varying it should be considered active because TCS invocations themselves can read each others' outputs. Bug: angleproject:5557 Tests: KHR-GLES32.core.tessellation_shader.tessellation_shader_tc_barriers.barrier_guarded_*_calls Change-Id: Ic252c0afff43a68828ee4cf5f4ba890b1b67731e Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2770679 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Mohan Maiya <m.maiya@samsung.com>