D3D11: Consolidate DSV allocation. This uses the new classes introduced in ResourceManager11. Smart pointers mean we can use ANGLE_TRY in more places, and don't need to manually release these views. There is now a single point in the D3D11 back-end where depth stencil views are allocated. BUG=angleproject:2034 Change-Id: If0de2529ece1298e8babf24c07cc4be9849cc4de Reviewed-on: https://chromium-review.googlesource.com/503249 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>