isBelow

Check whether the receiver (this) is below the given other channel in the channel list.

This function attempts to calculate this the same way the Discord client does:

• Channels outside a category are always at the top.

• Compare channels within the same category (or both at the top) by position.

• Compare parent categories by position.

This function throws an exception if the comparison doesn't make sense. This shouldn't ever happen unless Kord's type system breaks.