The ligature disabling code has been manually verified, but I was unable
to reftest it. (The only way I could think of would be to create an
Ahem-like font with a ligature table, but that would be an awful lot of
work.)
Near as I can tell, the method used to apply the spacing (manually
inserting extra advance post-shaping) matches Gecko.
r? @SimonSapin
Source-Repo: https://github.com/servo/servo
Source-Revision: 914f27263d60ffcbe2fd1f9e47a48e3aa3f1cd76
