Fix some international keybindings (#2957)

This adds primitive interaction with the IME system for keyboard
shortcuts in zed.

- Consult the IME functionality when handling keyboard shortcuts. This
allows you to bind to characters (like " on a Brazillian keybaord, or $
on a Czech keyboard) that aren't typed with an unmodified key.
([#1981](https://github.com/zed-industries/community/issues/1981))
([#1913](https://github.com/zed-industries/community/issues/1913))

Co-authored-with: Antonio Scandurra <me@as-cii.com>

crates/gpui/src/platform/mac/window.rs

@@ -1006,7 +1006,40 @@ extern "C" fn handle_key_event(this: &Object, native_event: id, key_equivalent:
                         .flatten()
                         .is_some();
                 if !is_composing {
-                    handled = callback(Event::KeyDown(event));
+                    // if the IME has changed the key, we'll first emit an event with the character
+                    // generated by the IME system; then fallback to the keystroke if that is not
+                    // handled.
+                    // cases that we have working:
+                    // - " on a brazillian layout by typing <quote><space>
+                    // - ctrl-` on a brazillian layout by typing <ctrl-`>
+                    // - $ on a czech QWERTY layout by typing <alt-4>
+                    // - 4 on a czech QWERTY layout by typing <shift-4>
+                    // - ctrl-4 on a czech QWERTY layout by typing <ctrl-alt-4> (or <ctrl-shift-4>)
+                    if ime_text.is_some() && ime_text.as_ref() != Some(&event.keystroke.key) {
+                        let event_with_ime_text = KeyDownEvent {
+                            is_held: false,
+                            keystroke: Keystroke {
+                                // we match ctrl because some use-cases need it.
+                                // we don't match alt because it's often used to generate the optional character
+                                // we don't match shift because we're not here with letters (usually)
+                                // we don't match cmd/fn because they don't seem to use IME
+                                ctrl: event.keystroke.ctrl,
+                                alt: false,
+                                shift: false,
+                                cmd: false,
+                                function: false,
+                                key: ime_text.clone().unwrap(),
+                            },
+                        };
+                        handled = callback(Event::KeyDown(event_with_ime_text));
+                    }
+                    if !handled {
+                        // empty key happens when you type a deadkey in input composition.
+                        // (e.g. on a brazillian keyboard typing quote is a deadkey)
+                        if !event.keystroke.key.is_empty() {
+                            handled = callback(Event::KeyDown(event));
+                        }
+                    }
                 }
 
                 if !handled {