CVE-2020-25717 winbindd: allow idmap backends to mark entries with ID_[TYPE_WB_]REQUI...

CVE-2020-25717 winbindd: allow idmap backends to mark entries with ID_[TYPE_WB_]REQUIRE_TYPE

This must only be used between winbindd parent and child!
It must not leak into outside world.

Some backends require ID_TYPE_UID or ID_TYPE_GID as type_hint,
while others may only need ID_TYPE_BOTH in order to validate that
the domain exists.

This will allow us to skip the wb_lookupsids_send/recv in the winbindd parent
in future and only do that on demand.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14539

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Gary Lockyer <gary@catalyst.net.nz>
BUG: https://bugzilla.samba.org/show_bug.cgi?id=14556

(cherry picked from commit 493f5d6b078e0b0f80d1ef25043e2834cb4fcb87)