[suggestion] Have practice checkpoints work in a limited state on updated levels

[Aktimoose]

Is your feature request related to a problem? Please describe.
Currently, whenever a level updates, all practice checkpoints on a layer are just completely nullified. This can get a bit frustrating as I would need to replace all of them with another practice run.

Describe the solution you'd like
Obviously it makes sense that the checkpoint cannot be saved in its entirety if a level updates, but I think that if a level updates then there should be an option for the saved checkpoints to be significantly more limited, only tracking player position, momentum, speed, and gamemode. They would essentially just be start positions just placed in the spots the checkpoints were originally.

[Kevadroz]

Yeah, that should be possible, but it would make that layer read only, unfortunately.

Added to the 1.4 Milestone