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.
