[Draft] [WIP] Experimental pinch-zoom support on iOS

I removed the `user-scalable=no` enforcement on the viewport.
This means that now the entire viewport is zoomed when you pinch/pan with two fingers.

I've attempted some CSS transforms on the toolbar during `touchmove`. This is very experimental and it is possible to keep the toolbar near the top of the screen where one expects it before, after, and during the gesture. It looks a bit jittery but is not too bad IMO.

Caret positioning is perfect, but apparently not the event-trap positioning after pinch-zoom, need to fix that.

Catch: popup menus are not children of the toolbar, and I cannot rescale them very easily. Would be nice if we had more control over these widgets.