This is implemented by seeing if a data-detected item is at the very
end of a truncated string, in which case it isn't trusted to be
complete. This applies not only to URLs, but to other data-detected
items as well like emails and addresses. It's also specific to
truncated text since a user could very well type an ellipsis in their
actual message, and *that* shouldn't prevent linkification.
It's possible that an item at the very end of a truncated string *is*
complete (i.e. the truncation point was just *after* the URL), but we
can't be sure without comparing to the full text or storing additional
information, and that's trickier for a number of reasons. The user can
still expand the message and get the linkification in this case.
