Add wgpu::RenderBundle::SetLabel

It was missing on just this object (and adapter/instance but that's
expected).

Bug: None
Change-Id: I865609b8194c872c16ad5590eaf0461751a56eab
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/134502
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>

dawn.json

@@ -1831,7 +1831,16 @@
     },
 
     "render bundle": {
-        "category": "object"
+        "category": "object",
+        "methods": [
+            {
+                "name": "set label",
+                "returns": "void",
+                "args": [
+                    {"name": "label", "type": "char", "annotation": "const*", "length": "strlen"}
+                ]
+            }
+        ]
     },
 
     "render bundle encoder": {