ProblemFactChange: allow refreshing/nuking all shadow variables

Suppose we have a shadow variable C which is the sum of A and B.
A is problem property (on a problem fact for example)
B is a genuine variable.
When a ProblemFactChange changes A, it also needs to update C somehow.

It should be possible to just "refresh all shadow variable" by triggering all shadow variable listeners for all shadow variables (aka "nuke them").

Besides in ProblemFactChange, this is also useful when unmarshalling an initialized solution when the shadow variables aren't persisted to safe room.