Auto merge of #25463 - Manishearth:input-mocking, r=asajeffrey

Add input mocking, input sources change event

Depends on  https://github.com/servo/webxr/pull/118

Also fixes some bugs I found.

Wanted to finish and merge this before I started on hit testing since the transient hit test stuff might have overlap.

There are a bunch of missing mock pieces that I'll probably do in a separate PR.

Still need to run tests.

Some things I skipped:
 - Doing handedness/target ray setting: See https://github.com/immersive-web/webxr-test-api/issues/46 , this would require making our impl support these changing
 - Handling button initial state: Would require some mock changes, but I ran out of time
 - Handling profiles/etc: We don't yet have impl support for these

r? @jdm

components/script/dom/bindings/trace.rs

@@ -534,7 +534,8 @@ unsafe_no_jsmanaged_fields!(
     webxr_api::Registry,
     webxr_api::Session,
     webxr_api::Frame,
-    webxr_api::InputSource
+    webxr_api::InputSource,
+    webxr_api::InputId
 );
 unsafe_no_jsmanaged_fields!(ScriptToConstellationChan);
 unsafe_no_jsmanaged_fields!(InteractiveMetrics);