Run conditions for specific state transitions

[ItsDoot]

What problem does this solve or what need does it fill?

I want to be able to run some cleanup logic only during a specific state transition.

What solution would you like?

Access to either previous_state + current_state, or current_state + next_state during an on_exit system.

What alternative(s) have you considered?

Currently my cleanup logic is held in the system that starts the state transition.

Additional Notes

The short discussion in discord, prior to filing this issue: https://discord.com/channels/691052431525675048/742569353878437978/1074101538802389012

[LiamGallagher737]

Also looking for something like this.

I like the idea of something like

.add_system_to_schedule(OnChange(GameState::A, GameState::B), my_system)

Though it's not very clear if this goes one or both ways. Something like OnTransition may work better.