A better way to check font rendering

In light of https://github.com/googlefonts/fontbakery/issues/3413, now may be a good time to discuss the future of generating font render samples. Atm, we rely on Browserstack screenshots to generate diff images. It's a great service but it has the following issues:

- Expensive (screenshot licence is around $120 a month so hobbyists won't want to pay this)
- Desktop browsers haven't been updated since 2018
- Slow
- It often times out so you don't get any results back

A better approach may be for us to write a tool that generates sample text for the user's current platform. We could then use this tool on github actions on all the different platforms we care about so for Win it will render text using DW and GDI, for Linux it will use FreeType and for Mac (if they have mac runners) CoreText/CoreGraphics. Credit to Simon since I've spoken to him about this idea before.

cc @simoncozens, @anthrotype, @felipesanches @madig