Auto merge of #27429 - asajeffrey:webxr-user-intent-pref, r=Manishearth

Add a pref to indicate user intent to enter webxr

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Add a pref to indicate that the user has indicated intent to enter webxr.

---
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes do not require tests because it's a command-line pref

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ports/gstplugin/servowebsrc.rs

@@ -218,6 +218,7 @@ impl ServoThread {
             None => Some(webrender_swap_chain),
             Some(..) => {
                 set_pref!(dom.webxr.sessionavailable, true);
+                set_pref!(dom.webxr.unsafe_assume_user_intent, true);
                 servo.handle_events(vec![WindowEvent::ChangeBrowserVisibility(id, false)]);
                 None
             },