Convert Matrix IDs into clickable Matrix URI scheme links

[jelv]

Toots containing Matrix IDs should be easy to open in your Matrix client. Just like we now convert URLs to clickable links. The Matrix URI scheme matrix-org/matrix-spec-proposals#2312 is now being finalized to replace matrix.to, so I'm opening this request to discuss it. Should we support converting known Matrix IDs in toots to clickable Matrix URIs?

My suggestion is to support the following Matrix IDs:

@user:example.org 
#alias:example.org 
!room:example.org
$event:example.org
(+spaces:example.org is not in the spec but it's expected to be added later)

I'm not sure if these type of ids are currently also in use for other platforms. That is something we should consider.