Rollback UI

[franknoirot]

Important

This is currently in planning, see discussion below.

Add two UX cases where the "hidden" mode of "keep on truckin" execution is enabled, once implemented:

1. Add a small draggable bar to the feature tree that users can slide up in the execution order and mark an operation beyond which no more engine commands should be sent, so they can see the model as if no more operations were added.
2. Amend the edit flow logic so that while in an edit workflow the state of the part is rolled back, and when the workflow is cancelled or completed the rollback is lifted

This does not need to be durable within the KCL, even though TradCAD does make it durable within the persisted project state. We will revisit later once we can address the implications durable rollbacks would have on large assemblies and team projects.

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Milestone for issue tracking: https://github.com/KittyCAD/modeling-app/milestone/20

[pierremtb]

Linked big dependency item #5189 to the corresponding milestone