Custom blocks: cleaning up & rerendering vanilla blocks

[YousefED]

Couple of leftovers from the Custom Blocks PR:

• [x] for non-react custom blocks, there's no way to clean up event handlers (react blocks can do this with a normal useEffect
• [ ] for non-react custom blocks, there's no way to reuse the existing DOM, a new DOM is always created
• [x] for both react and non-react, this issue prevents proper cleanup: https://discuss.prosemirror.net/t/nodeview-update-and-destroy-methods/5539/3, fixed in https://github.com/TypeCellOS/BlockNote/pull/223