Pills, autocomplete, etc all don't work without alias events

[turt2live]

The spec says we shouldn't rely on m.room.aliases, but we need them to render pills.

[turt2live]

Also the cache becomes outdated when aliases change, so pointing at a new room doesn't work.

[turt2live]

also affects autocomplete.

[richvdh]

on the subject of pills: related to #430

[ara4n]

why do we need m.room.aliases to render pills?

[turt2live]

So that when someone sends <a href='https://matrix.to/#/!roomid:exmaple.org'>text</a> it shows #matrix:matrix.org.

[richvdh]

also also: you can't set a new room to "anyone can join":

[richvdh]

aiui: the current plan here is to forge ahead with #12337

[bwindels]

So which alias should we use for pills? The canonical alias, if any, otherwise the first of alt_aliases, if any?

[bwindels]

for autocomplete: complete for all aliases (alt_aliases, canonical, and local aliases)
for pill: first canonical, then alt_aliases, then probably local aliases

[turt2live]

^this should be pretty much what we already do ftr

[bwindels]

After some discussion on #msc2432:matrix.org, I didn't add local alias support to pills and autocomplete. The label of a pill will be left alone though for a local alias and will still appear in a pill (albeit without avatar), see linked PRs.