feat: live-update cell highlighting

[jimniels]

When you reference cells using getCells you have to run the code to see the dashed outline highlighting what cells are being read.

https://github.com/quadratichq/quadratic/assets/1316441/1d8d345d-ba2e-4b5f-b66c-7062671f8ec7

Would be a much better experience if we could highlight this as you changed the cell reference. Otherwise the only way to know you've selected the right thing is to run the code first

[ddimaria]

@jimniels since there are cases where simple regex parsing of the values doesn't work (e.g. when the coords are variables), we decided to only show highlighted cells after a code run (via cells_accessed).

[jimniels]

Makes sense — but I still want it ha.

I would expect the software to be smart enough to figure out that if the values are static then it'll highlight them as I change it.

But if they're dynamic (i.e. variables) getting no highlights would feel expected.

[davidkircos]

Yeah I agree with Jim, but don't think this is really a high priority atm