Fix assorted linux issues (#10061)

- Fix a bug where modifiers would be dispatched before they changed
- Add a secondary modifier
- Improve keybindings

Release Notes:

- N/A

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

@@ -279,7 +279,7 @@ impl MacPlatform {
                         let mut mask = NSEventModifierFlags::empty();
                         for (modifier, flag) in &[
                             (
-                                keystroke.modifiers.command,
+                                keystroke.modifiers.platform,
                                 NSEventModifierFlags::NSCommandKeyMask,
                             ),
                             (