Rename fascist_firewall_* functions to reachable_address_*

In #17840 (moved) and #9067 (moved) / #9068 (moved), we unified ReachableAddresses and ClientUseIPv4/ClientUseIPv6/UseBridges. We'd previously unified FascistFirewall, FirewallPorts and ReachableAddresses.

This means that the functions called fascist_firewall_* should probably be renamed to be more descriptive.

I think reachable_address_* is one option, but let's follow typical naming standards and not repeat words in names:

• fascist_firewall_choose_address_dir_server ->
• reachable_address_choose_address_dir_server ->
• reachable_address_choose_dir_server

Let's also use this as an opportunity to disambiguate fascist_firewall_choose_address_impl & fascist_firewall_choose_address_base.