chore(state): cross-port latest changes from snapd's overlord/state

[dmitry-lyfar]

There are several major changes to the state package:

• Add WaitStatus support that allows a task to wait until further action to continue its execution. The WaitStatus is treated mostly as DoneStatus, except it is not ready status.
• Add Change.AbortUnreadyLanes.
• Add Change.CheckTaskDependencies to check if tasks have circular dependencies.
• Add task and change callbacks invoked on a status change.
• Update clients of the State.Get to use a new NoStateError to check if a desired key is present.
• Take StartOfOperationTime as a Prune parameter.