[gtk] (3 commits) Non-fast-forward update to branch ngl-vertex-attributes

[Matthias Clasen <matthiasc src gnome org>]

The branch 'ngl-vertex-attributes' was changed in a way that was not a fast-forward update.
NOTE: This may cause problems for people pulling from the branch. For more information,
please see:

 https://wiki.gnome.org/Git/Help/NonFastForward

Commits removed from the branch:

  156677e... gsk: Give ngl its own shader sources
  6869214... ngl: Set color and alpha as vertex attributes

Commits added to the branch:

  166922a... gsk: Give ngl its own shader sources
  41c56d6... ngl: Set color and alpha as vertex attributes
  8bc556b... Undo the vertex attribute for alpha