`wezterm.font` and `wezterm.font_with_fallback` can now specify
harfbuzz_features and freetype load/render target and flags as
options on a per-font basis.
This allows you to do things such as adjust shaping (eg: ligatures) or
rendering (eg: disable bitmaps, or adjust hinting) for a single font in
a fallback rather than globally for all fonts.