Vulkan backend render targets don't allow client to specify stencil bits

We already always create the stencil buffer even for wrapped RTs.

Make VulkanWindowContext use SkSurface::MakeFromBackendRenderTarget.

Change-Id: I5df429d347331801954ec17cb9d75e323a7af345
Reviewed-on: https://skia-review.googlesource.com/113206
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
4 files changed