Unified Undo/Redo for both Canvas and Text operations

[lihebi]

We indeed need a unified undo/redo to handle both canvas (Reactflow) and text (Monaco and Remirror) operations, as suggested by @forrestbao.

This needs to be done with Yjs UndoManager to support collaboration.

Note that undo/redo is a separate feature from a history/VCS system. Undo/redo is supposed to work in a short period of time within the browser session.