ClutterFixedLayout is the default layout manager for ClutterActor.

Existing subclasses of ClutterActor will get a fixed layout manager
regardless of whether they are going to use it, but since it sets the
CLUTTER_ACTOR_NO_LAYOUT flag, it will introduce regressions on actors
that perform their own layout management.

The CLUTTER_ACTOR_NO_LAYOUT flag was a bit of a mistake in the first
place, as it was introduced as a last minute workaround in the 1.0
process to deal with broken stuff in Moblin. It's going to be a target
for deprecation towards a removal when we start the 2.0 process.