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/+/2770679Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Mohan Maiya <m.maiya@samsung.com>