Added in c2013865d7,
this migration was supposed to only turn off the hashtag
setting for existing sites (since that was the old default)
but its doing it for new ones too because we run all migrations
on new sites.
Instead, we should only run this if the first migration was
only just created, meaning its a new site.
Follow up to a review in #18937, this commit changes the HashtagAutocompleteService to no longer use class variables to register hashtag data sources or types in context priority order. This is to address multisite concerns, where one site could e.g. have chat disabled and another might not. The filtered plugin registers I added will not be included if the plugin is disabled.
In both ChatMessage#rebake! and in ChatMessageProcessor
when we were calling ChatMessage.cook we were missing the
user_id to cook with, which causes missed hashtag cooks
because of missing permissions.
