[UI] add Safari-style zoom out tab strip, zoom in content

[o0101]

This is a nice new feature on Safari where a zoom gesture leads to the tab strip when zooming out and content when zooming in. We could easily implement this client side.

### Tasks
- [ ] track zoom gesture in and out, ensure consistency across mouse wheel and zoom
- [ ] isolate UI from changing on zoom gesture (don't shrink or expand browser UI chrome or other UI elements). Ideally use CSS
- [ ] link the zoom out with a tab strip overview (we have all the latest tab images available in the client side data structures)
- [ ] link the zoom in to zoom in to content centered under pointer (this should just be a zoom op on the img/canvas we use for viewport, potentially even just using css filter/transform op)
- [ ] refine the UX and remove any bugs

[o0101]

Use this branch for development:

git fetch origin
git checkout 290-ui-add-safari-style-zoom-out-tab-strip-zoom-in-content