This affects Messageable.history, ScheduledEvent.users,
Client.fetch_guilds, and Guild.audit_logs.
To illustrate the problem, Messageable.history counted returned
messages to tell when to stop iteration, but did so before filtering
away those past the before or after boundaries. When both
oldest_first=False and an after boundary were provided, this led to the
history iterator continuing to retrieve messages older than the after
boundary, which would then all be filtered away, continuing until the
message limit or the beginning of the entire channel was reached.
A similar situation would also occur with oldest_first=True and a
before boundary provided.
This commit changes the logic in these methods to count items after
filtering, so they stop requesting more as soon as the in-bounds items
are exhausted.
This affects Guild.create_scheduled_event and ScheduledEvent.edit
Previously, you would always be required to pass it in. However, it
makes sense to not repeat yourself if you already know it's a stage
channel or a voice channel due to the type information.
