First patch in of series that will rearrange the layout of the glyph instance attributes so that it matches brush instances.
This will be needed to add a unified shader that can render the most common alpha pass primitives, including text.

Differential Revision: https://phabricator.services.mozilla.com/D51879

[wrupdater] From https://hg.mozilla.org/mozilla-central/rev/570d5ec05d035d9fb156c8cc336ad66885b21de6