Pixel shader UAV barrier

[3Shain]

Even with Metal hazard tracking, a proper barrier between two draw calls that access UAV in pixel shader should be still inserted (or split the render pass).

Currently this breaks TieBrake the oficial ATP WTA game

Side note: [encoder memoryBarrierWithScope: MTLBarrierScopeTextures afterStages:MTLRenderStageFragment beforeStages:MTLRenderStageFragment] actually worked, even it's forbidden per documentation. Otherwise another possible solution is to insert an empty tile draw.