* The split_portals config option is finally respected.
* This should prevent future room duplication when migrating from the
pre-bridgev2 version of the bridge, as we'll finally address guild
channels properly (that is, without a Receiver set, unless
split_portals is true).
In the same vein as mautrix-whatsapp, -slack and others, do not make
assumptions about how the ID is represented in the connector code. Let
the discordid package be entirely responsible.
