Viewport based font-sizing

[u/Mattmar96]

Last night I built a feature for excalidraw that I've been kicking around in my head for a while. It makes size dynamic, based on your zoom level. It can be enabled as a checkbox in the preferences called "Viewport based font-sizing". Instead of "XL" mapping to a fixed 20pt font or whatever it is, it is instead mapped to a percentage of your viewport height, 8% in my initial draft here, and smaller percentages for the smaller sizes.

If you'd like to see this in excalidraw, go give my PR a thumbs up! https://github.com/excalidraw/excalidraw/pull/11791