CommandBufferResourceUsage: track render and compute separately.

This change is a preparation for making the compute pass track the
synchronization scope usages per dispatch instead of for the whole pass.

 - Split the tracking of render and compute passes usages.
 - Rename PassTextureUsage to TextureSubresourceUsage since is it not
   per-pass
 - Add SyncScopeResourceUsage as a subclass of PassResourceUsage to
   start modifying some of the code to work with synchronization scopes
   (even if syncscope == pass at the moment).

There are no functional changes.

Bug: dawn:632
Change-Id: Ieeb6d70a44dc1c726f26989eebcd87e63e732785
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/49883
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

src/dawn_native/ComputePassEncoder.cpp

@@ -55,7 +55,8 @@ namespace dawn_native {
 
                 return {};
             })) {
-            mEncodingContext->ExitPass(this, mUsageTracker.AcquireResourceUsage());
+            mEncodingContext->ExitPass(this, mUsageTracker.AcquireResourceUsage(),
+                                       PassType::Compute);
         }
     }