Changing subscriptions results in flickering with experimental bag player

[jtbandes]

When using the experimental bag player, changing subscriptions (e.g. typing in the message path input in a Raw Message panel) causes existing panels to flicker as they re-backfill their data.

Video shows first the old bag player, and then the new experimental player:

Screen.Recording.2022-03-29.at.4.54.33.PM.mov

[defunctzombie]

I think its because of this line: https://github.com/foxglove/studio/blob/main/packages/studio-base/src/players/IterablePlayer/IterablePlayer.ts#L319