Should text-shadow as outline consider font-weight?

In #2627, we're allowing text-shadow to serve as an outline, as long as it is less than 0.1em thick. I think it might be good for this not to be a static value, but a value that's relative to the font-weight. Bold text leaves less space between / within letters that a text-shadow can fill while remaining readable.

This needs to be tested first. I haven't confirmed this creates a problem, but I suspect there are false negatives that can come from this.