D3D12: Support per plane views with NV12 textures

Adds support for NV12 texture format and per plane view aspects.
Only allows planar sampling of imported DX11 textures. See usage
tests for examples and formats.h for rules.

Bug: dawn:551
Change-Id: I44b89d2c07bb9969638e77ce7c756ef367167f0c
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/38781
Commit-Queue: Bryan Bernhart <bryan.bernhart@intel.com>
Reviewed-by: Austin Eng <enga@chromium.org>
diff --git a/src/dawn_native/vulkan/UtilsVulkan.cpp b/src/dawn_native/vulkan/UtilsVulkan.cpp
index b379e25..7e58319 100644
--- a/src/dawn_native/vulkan/UtilsVulkan.cpp
+++ b/src/dawn_native/vulkan/UtilsVulkan.cpp
@@ -65,6 +65,8 @@
                     flags |= VK_IMAGE_ASPECT_DEPTH_BIT | VK_IMAGE_ASPECT_STENCIL_BIT;
                     break;
 
+                case Aspect::Plane0:
+                case Aspect::Plane1:
                 case Aspect::None:
                     UNREACHABLE();
             }