CommandReconciler.revert keeps its name

The contract of revert(pending) is: make replaying pending after the incoming command correct, or return false to ask for a snapshot. DocumentReconciler and voxel-map's VoxelReconciler roll back; pixel-art and blockset return true and do nothing, because absolute writes replay over anything. The contract is documented instead of renaming the method to rewind.

SyncedCommandDocument stays: it adapts DocumentSyncClient to editor.host's SyncedDocument (document, ready as a promise, dispose).

Considered Options

• Rename to rewind. Closer to what two of four implementations do, wrong for the other two, and a break in every reconciler.