This commit adds a new `/hashtag/search` endpoint and both
relevant JS and ruby plugin APIs to handle plugins adding their
own data sources and priority orders for types of things to search
when `#` is pressed.
A `context` param is added to `setupHashtagAutocomplete` which
a corresponding chat PR https://github.com/discourse/discourse-chat/pull/1302
will now use.
The UI calls `registerHashtagSearchParam` for each context that will
require a `#` search (e.g. the topic composer), for each type of record that
the context needs to search for, as well as a priority order for that type. Core
uses this call to add the `category` and `tag` data sources to the topic composer.
The `register_hashtag_data_source` ruby plugin API call is for plugins to
add a new data source for the hashtag searching endpoint, e.g. discourse-chat
may add a `channel` data source.
This functionality is hidden behind the `enable_experimental_hashtag_autocomplete`
flag, except for the change to `setupHashtagAutocomplete` since only core and
discourse-chat are using that function. Note this PR does **not** include required
changes for hashtag lookup or new styling.
7c25597da2