Consider a generic typescale

Now that Stacks has matured and adoption has grown, I find myself visiting the documentation most for our type size. I just can't seem to internalize if something is a fs-headline1 or a fs-display2.

I find the motivations for doing so were to be a bit more prescriptive in our type scale, but in practice, if someone knows their type is at 21px, they're going to go to our typography page and choose the size that matches 21px. I don't know what it is without looking.

Here's what I propose.

Our font sizes should be literal. We should alias / rename our current type sizes with fs-[xx]. This could be more in line with how we represent width and padding, eg fs-11 meaning font-size: 11px or we could setup our typescale from 1–9, 1 being the smallest, and 9 being the largest.

Either way, it will be much easier to step through the type scale as we're implementing designs than constantly trying to figure out what class name 21px is.

Start with the typography page and the existing fs-headline1 and fs-display2 type-size names, then compare them with the width and padding naming conventions mentioned in the issue. Done requires an agreed generic scale or literal naming scheme and updated type-size documentation and classes to match it.