Auto merge of #23707 - servo:jdm-patch-31, r=paulrouget

Ensure GL context is prepared for deinitialization.

I tested shutdown on Windows numerous times before and after this change, and I have not seen any further panics in debug builds in builds with the GL context made active before deinitializing WebRender.

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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 fix #23706 and fix #23614.
- [x] These changes do not require tests because no tests on windows ;_;

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components/compositing/compositor.rs

@@ -353,6 +353,7 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
     }
 
     pub fn deinit(self) {
+        self.window.prepare_for_composite();
         self.webrender.deinit();
     }