Opportunistically recalculate remembered sets for almost-eager reclaim candidates

Selection of eager reclaim candidates is based on the number of remembered set entries.

This is a fixed threshold, if the number of entries in the card remembered set is larger than that, we never try to eager reclaim that region.

Marking already rebuilds the remembered sets for those, but marking rounds can be far apart. Maybe it is useful to flush the remembered sets of a few of these near-candidates into the DCQ regularly to see whether something changed?