Support checkpoints in expanding void levels

[wjt]

Suppose you have a level which has a series of islands:

(Imagine that the template enemies are void-spreading enemies which chase you, but can't cross the bridges.)

You successfully escape the first one, and get to the checkpoint:

Then you get caught on the second island:

Currently, you would respawn at the checkpoint, but the void covering the first island would be gone:

This is because we only save a very small amount of state: current scene and current checkpoint.

We can work around this through level design, like we do in ink combat scenes: break the level into 3 scenes so that changing scene acts as a checkpoint. But it would be nice for this to work properly. To do so we'd probably need a more general state-saving mechanism that different elements of the scene could plug into.

XP Summary (total 375)

Subdomain	Skill	XP
Engineering: Gameplay & Systems Programming	Problem Solving	150
Engineering: Gameplay & Systems Programming	Creativity & Design Thinking	75
Engineering: Gameplay & Systems Programming	Technical Literacy	150

[wjt]

I think it would make sense to wait on the resolution of:

• Add signal when collectible is collected(?) #784

before tackling this, because both will involve fleshing out how state is saved and loaded.

[manuq]

As the description says, the easiest way to work-around this is by splitting the chasing in 2 scenes.