Include TODOs in Calendar.timeline

[rafalkrupinski]

Is your feature request related to a problem? Please describe.
Calendar.timeline shows only events, while it has also other types of components, including recurrent ones, like VTODO or VAVAILABILITY

Describe the solution you'd like
There's should be a way to produce a timeline for other types of components, either together in def timeline or in separate methods (event_timeline, todo_timeline, etc), or both.

Describe alternatives you've considered
I can duplicate existing code to apply it to todos

Additional context
Conceptually other components are also part of timeline, maybe not necessarily instabilities or alarms, but that depends on use-case.
I'm volunteering to work on this.

[allenporter]

There is a generic_timeline API which I think either can support this or can be extended to support this -- here is an example of getting journal items on a timeline:
https://github.com/allenporter/home-assistant-journal-assistant/blob/0c484adc6b0b6bbbc26017bbcda8ec511b6c8885/custom_components/journal_assistant/calendar.py#L68

So perhaps we could:
(1) verify this works for todo, or extend if not -- just to get core functionality there
(2) consider evolution of the api to make it more streamlined.

[rafalkrupinski]

Yeah, I found generic_timeline later on and it works. I just thought Calendar.timeline suggest timeline of all items, but now I think that probably wouldn't make much sense from use-case perspective. But, yeah, api could be better in this regard. Perhaps timeline_of(type[Component])ortimeline_${component}`