Todo: fix mobile drag

Hi Tom, thanks for the useful editor. I was wondering, how can the `viewof` be made backwritable as to work with your https://observablehq.com/@tomlarkworthy/shareview?

attach to the .data subview, not the root dataeditor, something like share(viewof mydataeditor.data) selection is not backwritable ATM, tho it should be really

I am trying to get it working now

it kinda works in that changes to the quantities are remembered and propagated https://observablehq.com/d/3f62e88eeeac7418 selection is broken in a weird way and drag and drop doesn't work until quantity is changed[1]. [1] because data editor generates a synthetic input even and shareview syncs only human generated events. I'll add these to open issues and get back to them at some point. I am open to PRs too if you want things to move faster.

I fixed the drag and drop. Fixing selection is a bit more work which I will pass on for now.