Get rid of glm dependency?

[lhog]

Because the users of vrhi might use Eigen or their own matrix / vector implementation or something else. And it generally doesn't belong to the rendering platform middleware don't dealing with matrices or other advanced 3D constructs.

Most if not all usages of GLM are related to conveying 2D/3D dimensions, for which an array or tuple or initializer_list will work just fine.