Move vr_values out of vrp_prop into execute_vrp so it can be shared.

Move vr_values out of vrp_prop into execute_vrp so it can be shared.

vr_values is being shared among the propagator and the folder and
passed around.  I've pulled it out from the propagator so it can be
passed around to each, instead of being publicly accessible from the
propagator.

gcc/ChangeLog:

	* tree-vrp.c (class vrp_prop): Rename vr_values to m_vr_values.
	(vrp_prop::vrp_prop): New.
	(vrp_prop::initialize): Rename vr_values to m_vr_values.
	(vrp_prop::visit_stmt): Same.
	(vrp_prop::visit_phi): Same.
	(vrp_prop::finalize): Same.
	(execute_vrp): Instantiate vrp_vr_values and pass it to folder
	and propagator.