fetch: centralize logic to print remote URL

fetch: centralize logic to print remote URL

When fetching from a remote, we not only print the actual references
that have changed, but will also print the URL from which we have
fetched them to standard output. The logic to handle this is duplicated
across two different callsites with some non-trivial logic to compute
the anonymized URL. Furthermore, we're using global state to track
whether we have already shown the URL to the user or not.

Refactor the code by moving it into `format_display()`. Like this, we
can convert the global variable into a member of `display_state`. And
second, we can deduplicate the logic to compute the anonymized URL.

This also works as expected when fetching from multiple remotes, for
example via a group of remotes, as we do this by forking a standalone
git-fetch(1) process per remote that is to be fetched.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>