support msdf fonts for text rendering

https://soimy.github.io/msdf-bmfont-xml/ seems to be an excellent msdf generator (utf-8 support, good parameterization etc.). The glyph fragment shader needs to account for 4 channel distance fields instead of a single one.

- [ ] Implement switch to enable MSDF instead of SDF
- [ ] Implement simple example comparing both techniques side by side

Start with the glyph fragment shader and the linked msdf-bmfont-xml generator. Trace how the renderer currently handles SDF text, then implement the MSDF switch and add the requested side-by-side comparison example. Done means both SDF and MSDF rendering can be enabled and compared.

Written by the indexing model from the issue text.