Add hotkey to conditionally disable/enable snapping when pressed

[wade-cheng]

I believe it would be nice to have a hold-to-activate hotkey for turning off snapping, and this would probably be another adventure in hunting down parity across the tools. Google Slides and company has this last I used them, and it's nice to be able to precisely position objects without having to finnick around snap points that you don't want to follow.

We should discuss the design language. For one note, many modifier buttons are already taken for the drag tool. Google uses Alt.

[Keavon]

Assigning to myself since this requires design work for our keyboard mapping design language.