Swipe and sync between two maps

It would be cool to have a way to do "map comparisons" from Python. This would be along the lines of [mapbox-gl-compare](https://github.com/mapbox/mapbox-gl-compare):


On the JS side, this would take a bit of work. Primarily, I have to figure out how to:

- render two map views, either side by side or possibly above and below
- sync the view state between them
- render a basemap in both

I did a little test:
```jsx

It's nice that the deck.gl part is working, but not sure how to get the basemap to render in both.

On the Python side, the easiest way to do this would probably be to have a new `SplitMap` class that manages two sets of layers.

See also:

- https://github.com/visgl/deck.gl/discussions/7627