For actors which don't have needs_allocation set to TRUE and where the
new allocation wouldn't be different from the old one, the allocate()
vfunc doesn't have to be called. We still did this in case a parent
actor was moved though (so the absolute origin changed), because we
needed to propagate the ABSOLUTE_ORIGIN_CHANGED allocation flag down to
all actors.
Since that flag is now removed and got replaced with a private property,
we can simply notify the children about the absolute allocation change
using the existing infrastructure and safely stop allocating children at
this point.
https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1247