Include all headlines in Org agenda files and as well as all extra text search
files in interactive selections. To make this more managable, introduce a
dedicated function to query the user for a target item.
F9 is a comparably prominent key binding, and we now bind it to the more
important `db/org-add-link-to-other-item'. The formar binding to
`db/org-find-links-to-current-item' is bound to F11 now, since it will still be
used often, but not more often then inserting links (I think). The old binding
for F11 to `org-capture' has not been used much, and so we can dispense of it.
The main entry point is now `db/org-find-links-to-current-item', which decides
how to obtain the ID and CUSTOM_ID of the item to look for. The main work is
done by `db/org-find-items-linking-to-id', which does some checks, build the
query, and then calls `org-search-view' (which, indeed, does the actual work).
Users should call `db/org-find-links-to-current-item' only.
It is not clear what function really changes the matching data, but it's called
by `org-roam--id-link-face', and this is where we save the matching data now.
TODO: check whether this has been reported or even fixed upstream.
Neither logging information not tasks should be part of that file, so keeping it
in `org-agenda-files' is not really necessary. Indeed, it has only been
included in there to allow `org-search-view' to search that file. However, with
using `org-agenda-text-search-extra-files' makes this approach obsolete.