Auto merge of #27295 - asajeffrey:gstreamer-webxr, r=Manishearth

Gstreamer plugin support for streaming from webxr

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Allows us to stream webxr video content.

---
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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 we don't reftest the gstreamer plugin

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components/compositing/compositor.rs

@@ -1689,6 +1689,9 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
         // Run the WebXR main thread
         self.webxr_main_thread.run_one_frame();
 
+        // The WebXR thread may make a different context current
+        let _ = self.webrender_surfman.make_gl_context_current();
+
         if !self.pending_scroll_zoom_events.is_empty() && !self.waiting_for_results_of_scroll {
             self.process_pending_scroll_events()
         }