Auto merge of #12461 - andrewdavidmackenzie:enable-quit-keyboard-shortcut, r=ConnorGBrewster

Add a keyboard shortcut (Command + Q on Mac or Control + Q on other O…

<!-- Please describe your changes on the following line: -->
Added code in window.rs to enqueue the Window::Quit event when the Command/Control + Q keyboard shortcut is detected IF keyboard shortcuts are enabled.
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<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #12422 (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [X] These changes do not require tests because there are no tests able to test keyboard shortcuts at the moment

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ports/glutin/window.rs

@@ -917,6 +917,11 @@ impl WindowMethods for Window {
                     self.event_queue.borrow_mut().push(WindowEvent::Reload);
                 }
             }
+            (CMD_OR_CONTROL, Some('q'), _) => {
+                if let Some(true) = PREFS.get("shell.builtin-key-shortcuts.enabled").as_boolean() {
+                    self.event_queue.borrow_mut().push(WindowEvent::Quit);
+                }
+            }
 
             _ => {
                 self.platform_handle_key(key, mods);