Revert OperationFactory interface changes made in a1f86ac

By specifically invoking a new when creating an operation instance makes it quite difficult for external operation constructors, as there is no easy way for external ops to share non-document state.

All WebODF ops don't have this issue as new functions can easily be added to the OdtDocument interface to support the new requirements.

(For previous discussion on this particular change, see https://github.com/kogmbh/WebODF/pull/376#discussion-diff-9579662)