…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/2e0c9b9bd50759b80c9075c4ebb795a2031d4c35