Smooth zoom in 3D view

[emilk]

Scrolling the 3D view currently cause huge discreet jumps in zoom level:

The same is true for cmd-scrolling to zoom the 2D view.

We should be able to smooth this out somehow, but I'm not exactly sure how.

On a mac trackpad we get very smooth scroll/zoom evens, and we don't want to apply additional smoothing to that. So we need to somehow detect whether scroll input is coming from a smooth or discreet source.

This should be helpful:

• Add raw mouse wheel event emilk/egui#2782

[emilk]

Related, but slightly different, issue:

• Improve scroll-to-zoom on web #965