Keyboard shortcuts don't work when using UIKit for Mac (Project Catalyst)

I successfully added the f shortcut in my app by adding:

```objc
- (NSArray *)keyCommands {

UIKeyCommand *flexToggleCommand = [UIKeyCommand keyCommandWithInput:@"f" modifierFlags:kNilOptions action:@selector(onFLEXToggleCommandTrigger)];

return @[flexToggleCommand];
}

- (void)onFLEXToggleCommandTrigger {

[[FLEXManager sharedManager] toggleExplorer];
}
```

in `AppDelegate.m`, but I don't know how to add all of them directly in FLEX, hence I created an issue instead of a PR.