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.
The spacing between glyphs seems too wide. Need to figure this out.
A bunch of the integer vs float changes in this diff were a result
of trying to run this down, but success has been limited, and in fact
the spacing has increased as a result of making this more correct(!)
Initially I wanted to make the font code separate from
the main wterm executable in the hope that it would be
reusable. However, we do need to be able to reach in
to both the font implementation and the SDL texture
implementation in order to capture the glyph data
into textures, so let's just embrace it all being
in the same crate.
