Support MSDF/MTSDF fonts

[soywiz]

Would be nice to be able to generate them on the fly from TTFs/OTFs with a mutable atlas to add glyphs on the fly, so people can just use a normal TTF but render without intermediate textures for specific texts. While still being able to support normal TTF fonts normally rendered for static texts to have as much quality as possible.

References MSDF:

• https://github.com/Chlumsky/msdfgen
• https://github.com/Chlumsky/msdf-atlas-gen
• https://github.com/soimy/msdf-bmfont-xml
• https://levelup.gitconnected.com/msdf-font-rendering-in-webgl-91ce192d2bec
• https://medium.com/@calebfaith/implementing-msdf-font-in-opengl-ea09a9ab7e00
• https://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=9024910&fileOId=9024911
• https://steamcdn-a.akamaihd.net/apps/valve/2007/SIGGRAPH2007_AlphaTestedMagnification.pdf
• https://github.com/Chlumsky/msdfgen/files/3050967/thesis.pdf : 4.4 Direct multi-channel distance field construction

SDF:

• https://github.com/mapbox/tiny-sdf
• https://github.com/dy/bitmap-sdf
• https://github.com/dy/bitmap-sdf/blob/78de3569d32404a7009f62bea3befca55838118a/index.js#L90-L134
• https://cs.brown.edu/people/pfelzens/dt/

Later we should have also emojis in mind. Maybe emojis can be rendered alone in separate bitmaps/textures at a fixed size, and alternatively for COLRv1 fonts we can render vector chunks, and colorize them later.

[soywiz]

We can start implementing a SDF autoatlas as a proof of concept, since it should be easier and faster to implement, and there is already code in the codebase for that IIRC, then implement the MSDF later.

[soywiz]

• https://astiopin.github.io/2019/01/06/sdf-on-gpu.html
• https://github.com/mapbox/tiny-sdf