This is primarily for macos where the default freetype
installation is unable to render color emoji, but should also
help make things more consistent across the various platforms.
It's a little bit awkward on linux because the font-loader crate
pulls in the now-conflicting servo-font* crates. I've disabled
font-loader on linux systems; it's just calling fontconfig under
the covers anyway.
I've had mixed results with esctest; the IRM and cursor save/restore
tests fail for me in terminal.app, iterm2 and xterm, and fail in the
same way on wezterm, so I'm not sure if I'm not running those tests
correctly. However, they did encourage the discovery of some other
real issues in the wezterm emulation.
