…rmuizel,gw

Add annotations to vertex shaders so that SWGL can detect when a vertex attribute
is generated by per-instance data rather than per-vertex data.

Differential Revision: https://phabricator.services.mozilla.com/D65614

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/cf730c4e65393b07f842ab6f58c2509a1009f920