For prompt evacuation of unpinned pinned regions (or evacuation failed regions) in JDK-8140326 we need to determine whether to keep their remembered sets or not.

The important metric here is live bytes, i.e. number of bytes live after evacuation failure.

The JDK-8140326 change needs that metric at the start of the post evacuation phase (before post evacuation phase 1); currently we calculate this _in_ post evacuation phase 1 which is too late.

Change the code to use the existing marking infrastructure that collects live bytes for evacuation failed regions so that the result is available at the correct time for JDK-8140326