Make TextureAspect match WebGPU

It was changed from a bitmask to an enum. It isn't used in Dawn yet.

BUG=dawn:22

Change-Id: I13b39e0ea137fd24470cf23bb4bd94dfcaf66d19
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/8626
Reviewed-by: Yunchao He <yunchao.he@intel.com>
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

dawn.json

@@ -1006,11 +1006,11 @@
         ]
     },
     "texture aspect": {
-        "category": "bitmask",
+        "category": "enum",
         "values": [
-            {"value": 1, "name": "color"},
-            {"value": 2, "name": "depth"},
-            {"value": 4, "name": "stencil"}
+            {"value": 0, "name": "all"},
+            {"value": 1, "name": "stencil only"},
+            {"value": 2, "name": "depth only"}
         ]
     },
     "texture copy view": {