We only use this in gsktransform.c
It uses the new CSS parser.
Also rename it from GskMatrixCategory to GskTransformCategory.
In particular, add a per-category querying API for the matrix: - gsk_transform_to_translate() - gsk_transform_to_affine() - gsk_transform_to_2d() - gsk_transform_to_matrix() This way, code can use the relevant one for the given category.
The renaming of the prefix makes this a large patch.
