Use the new Enso Font; also change the anti-aliasing logic to be based on device pixel ratio, rather than platform. This will improve the clarity of font rendering on Windows/Linux machines with high pixel densities.
Design reference:
Tested on various combinations of DPR/platform:
OS X, `devicePixelRatio` = 2 (should look similar to how we were already rendering *mplus1* on OS X):
<img width="1440" alt="Screenshot 2023-08-07 at 5 46 11 PM" src="https://github.com/enso-org/enso/assets/1047859/2fdf251a-ba5e-426f-b6c4-194347a9cee4">
Windows, `devicePixelRatio` = 1.25 (should look similar to how we were already rendering *mplus1* on this platform/DPR):
Linux, `devicePixelRatio` = 1 (should look similar to how we were already rendering *mplus1* on this platform/DPR):
# Important Notes
Style changes:
- Use the Enso Font for code in Rust, replacing the DejaVu fonts.
- Use the Enso Font in HTML: code in documentation, and error visualizations.
- Change SpanWidgets from Bold to Extra Bold, to match the design.
Implementation improvements:
- The new font download is cached (and Github-authenticated); this should eliminate a "rate limit" build failure I've
encountered in the past.
- Clean up DocSection HTML rendering a bit.
- Remove a CSS file that seems to have been superseded.
