Optimized the chat so that resuming PiP does not cause stutters.
This new implementation makes it so that only the latest (100) messages are
rendered at any given time, rather than every single one.
Once autoscroll is disabled and we scroll up in chat, the most recent
messages will be added to a buffer to prevent shifting.
Essentially, I've made it so that the default chat shows only the (100)
most recent messages. When you want to scroll back, the chat will
silently switch to the version with the last (10000) messages, giving
the best of both worlds in performance and scrollback history.
932412b75f