Deprecate TextureDescriptor::arrayLayerCount -> size.depth

This updates CL:

 - Adds a deprecation warning to use size.depth instead of
arrayLayerCount.
 - Changes all tests and samples to use size.depth.
 - Adds deprecation tests for the change.

In particular the state tracking in TextureBase isn't changed yet
because it requires non-trivial changes in the backends. It will be done
in a follow-up CL.

Bug:dawn:22

Change-Id: Ic02dfb5baaba8d5b06cd339ce988e9b1d16cb5e9
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/23101
Reviewed-by: Jiawei Shao <jiawei.shao@intel.com>
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

src/dawn_native/opengl/TextureGL.cpp

@@ -28,7 +28,7 @@ namespace dawn_native { namespace opengl {
         GLenum TargetForTexture(const TextureDescriptor* descriptor) {
             switch (descriptor->dimension) {
                 case wgpu::TextureDimension::e2D:
-                    if (descriptor->arrayLayerCount > 1) {
+                    if (descriptor->size.depth > 1) {
                         ASSERT(descriptor->sampleCount == 1);
                         return GL_TEXTURE_2D_ARRAY;
                     } else {