feat(2d): add save and restore methods to nodes

[ksassnowski]

Description

This PR introduces two new methods save and restore to the base Node class. These methods allow us to save a snapshot of a node's current state, so that we can then later revert the node to this state.

As part of implementing the save/restore feature, I have also extracted more general getState() and applyState() methods.

• getState() returns a snapshot of the node's current state. The implementation is almost identical to how snapshotClone works, however, it does not include snapshots of the node's children.
• applyState take a map of signal values and applies them to the current node. If the signal does not exist on the node, it gets ignore.

This also fixes an issue inside deepLerp so it deals with booleans properly.

Closes #403

[aarthificial]

You should also clear the stack in the dispose method just to be safe.