Add support for webcal:// links

[strk]

Pitch

See https://en.wikipedia.org/wiki/Webcal

I've been trying to subscribe to an .ics URL and having a very frustrating evening. The attempt to use a webcal link was my last chance but neither Tusky nor Mastodon-Web recognized it as a link. I'm starting to request its support here first...

Motivation

Whoever wants to advertise a public calendar could use the webcal:// scheme to make it clear what the resource is about. The current alternative is to use an http(s) url but then the browser would need to react based on Content-Type ...

In any case, webcal is a IANA recognized scheme so I dont' see why it shoudn't be supported:
https://www.iana.org/assignments/uri-schemes/prov/webcal

[connyduck]

Tusky doesn't make any links clickable, that is always decided by the server. Changing this is not trivial and I think its nice if all clients have similar rendering behavior, so I'd rather not add this to Tusky.

[strk]

Ok then I now filed it here: mastodon/mastodon#34598

I'll let you decide if this here needs to be closed