Bug 1594091 - Move color_mode and subpx_dir to the first half of the …
…glyph instance z field. r=gw Depends on D51879 Differential Revision: https://phabricator.services.mozilla.com/D51880 [wrupdater] From https://hg.mozilla.org/mozilla-central/rev/e405048af859fb0b8aca0060ac8c0df5388ee630