actor: Add TransformInfo

actor: Add TransformInfo

ClutterTransformInfo is a (private) ancillary data structure that
contains all the decomposed transformation data, i.e. rotation angles
and centers, scale factors and centers, and anchor point. This data
structure is stored in the GData of the actor instance instead of the
actor's private data. This change gives us:

  • a smaller, cleaner private data structure;
  • no size penalty for untransformed actors;
  • static constant storage for the defaults, shared across all
    instances;
  • cache locality for all the decomposed transformation data,
    given that the structure size is smaller.

At the end of the day, the only authoritative piece of information for
actor transformation is the CoglMatrix that we initialize in
apply_transform() from all the decomposed parameters, and that can stay
inside the private data structure of ClutterActor.