Our previous list visibility resolver grabbed posts if either follower
collection of the user in a list who is followed is in `to` or if
follower collection of the user in a list was in `cc`. This not only
missed unlisted posts but also lead to leaking private posts when
`fix_explicit_addressing` mistakingly started putting follower collections
to `cc` (also fixed in this MR).
Reported by @kurisu@iscute.moe via a DM
d9c0650ff9