Cannot /join an auto-completed room alias

[kegsay]

I tried typing:

/join #neb

and saw #neb:matrix.org pop up, so I selected it with my mouse and then hit enter and a dialog appeared which said:

Command Error
Usage: /join #alias:domain

I'm guessing because the raw text is in markdown form by that point.

[lukebarnard1]

This would be fixed if we didn't insert MD on completion of rooms, much like #4674

The issue is that the draft-js-export-html will convert LINK entities to anchor elements for us, but currently the markdown conversion doesn't consider LINK entities at all. We can change it so that it converts LINKs to [links](some.url) before saving to history and sending the message.

[lukebarnard1]

because the raw text is in markdown form by that point.

correct

[lukebarnard1]

So instead of totally rewriting the RTE to either use entities with type MENTION or totally rewriting the RTE to always use the same AST for a given message (see #4679), I'm going to do the quick fix of stripping MD mentions before handling commands.