D3D11: Add support for multiview layered rendering A branch is added in the geometry shader to select either the viewport, or texture layer which is being rendered to based on the value of a uniform in the driver constant buffer. Using this approach there is no need for separate programs for side-by-side and layered rendering. BUG=angleproject:2062 TEST=angle_end2end_tests Change-Id: I66701164ff02a851c13695d5409f8ad350534e69 Reviewed-on: https://chromium-review.googlesource.com/645547 Commit-Queue: Martin Radev <mradev@nvidia.com> Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>