This commit moves router_pick_published_address() and the related helper
functions into the new file.

The log_addr_has_changed() function has been made public in router.h so we can
use it in relay_resolve_addr.c.

This is a refactoring as part of Sponsor 55. Only code movement at this
commit.

Part of #33789

Signed-off-by: David Goulet <dgoulet@torproject.org>