Add font-kit support

[cbrewster]

Continued from #1

Right now fonts are accessed via hard-coded paths. This is not portable, we should look into using fontkit.

[rofrol]

Plan

Remove usage of https://doc.rust-lang.org/std/macro.include_bytes.html with:

1. Load system monospace font with font-kit.
2. Convert it to wgpu_glyph::Font (compiler shows rusttype::Font).

Use this examples

• https://github.com/dhardy/kas/blob/f4b052203752d16f9aeb7b53b42a1c17b7189bf5/kas-wgpu/src/font.rs
• https://github.com/servo/font-kit/tree/master/examples

Documentation

• https://crates.io/crates/glyph_brush
• https://crates.io/crates/rusttype
• On Windows this loader https://github.com/servo/font-kit/blob/9c189cc8b6dd139b1d9bce4920d7788a7f27c076/src/loaders/directwrite.rs is used but is not in documentation https://docs.rs/font-kit/0.5.0/font_kit/loaders/?
• https://docs.rs/font-kit/0.5.0/font_kit/handle/enum.Handle.html
• https://docs.rs/wgpu_glyph/0.6.0/wgpu_glyph/struct.Font.html
• https://docs.rs/font-kit/0.5.0/font_kit/loaders/freetype/struct.Font.html
• https://docs.rs/rusttype/0.8.2/rusttype/struct.Font.html
• https://docs.rs/rusttype/0.8.2/rusttype/enum.SharedBytes.html

Other Examples

• https://github.com/linebender/skribo/blob/03c63ac17bb93e29f82e959dac94027935a21159/examples/render.rs#L21
• https://github.com/wez/wezterm/blob/4687b3bb48b49c0a1ffaade299aea0480ff3d488/src/font/locator/mod.rs#L116
• https://github.com/RazrFalcon/resvg/blob/0c1219667a27b39792c59fd24c1f628808f57d01/usvg/src/fontdb.rs#L313

Concerns/Alternatives

On my Windows box, font-kit takes just over a minute to compile and over 800k release code size. That seems high for something that's just loading fonts, but on the other hand I don't see any good way to get this down.

• https://www.reddit.com/r/rust/comments/b9mt2i/font_fallback_deep_dive/ek5ndmv/
  • https://raphlinus.github.io/rust/skribo/text/2019/04/04/font-fallback.html
• https://github.com/servo/font-kit/wiki/FAQ
• alternative https://github.com/MSleepyPanda/rust-font-loader
  • RFC: Font Configuration alacritty/alacritty#957 (comment)
• Add fontkit as a render backend alacritty/alacritty#1720 (comment)
• Investigate using font-kit alacritty/alacritty#1568

[cbrewster]

I prefer to avoid adding large dependencies, but for now this is probably the easiest approach to get the editor much more portable.
It may be worth revisiting this later as we probably won't be using everything font-kit has to offer.