Support optional injectHotkey

[erengeez]

injectHotkey supports passing a signal as a hotkey argument but it does not support undefined for the signal.

It would be useful if the hotkey is registered optionally based on the component/directive input:

public readonly optionalHotkey = input<RegisterableHotkey>();

constructor() {
    // Error: Argument of type 'InputSignal<RegisterableHotkey | undefined>' is not assignable to parameter of type 'RegisterableHotkey | (() => RegisterableHotkey)'.
    injectHotkey(this.optionalHotkey, () => { 
        //do actions
     });
}

Right now the only workaround I found is setting some random default hotkey and disabling it:

constructor() {
    injectHotkey(computed(() => this.optionalHotkey() ?? '\\'), () => {
        // do actions
    }, computed(() => ({ enabled: this.optionalHotkey() !== undefined })));
}

[KevinVandy]

You can do this today by returning an empty array when the input is empty. Since @tanstack/angular-hotkeys 0.14.0, an empty sequence registers nothing:

readonly optionalHotkey = input<RegisterableHotkey>()

constructor() {
  injectHotkey(() => this.optionalHotkey() ?? [], () => {
    // do actions
  })
}

The getter is reactive. The hotkey registers when the input gets a value and unregisters when it goes back to undefined. I'm leaving this open, because accepting undefined directly would be nicer.