Bug 1683084 - add SWGL fast-path for ps_split_composite shader. r=jrmuizel
Bug 1683084 - add SWGL fast-path for ps_split_composite shader. r=jrmuizel

Differential Revision: https://phabricator.services.mozilla.com/D102444

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/76681fef6b50b14d180cae3e5346697b78386d91

servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender