Increase the G1 eager reclaim candidate selection threshold

The selection of candidates for eager reclaim of humongous objects mostly depends on the number of remembered set entries for that humongous object.

Currently this threshold corresponds to the sparse prt entry count as gathering the number of remembered set entries for the higher level PRTs is considered too costly. This sparse prt entry count is very low, although it has increased in JDK-8223162.

However, with JDK-8233919 this operation is a read of a single variable. So the reason to keep the threshold low is gone.

Look into increasing this threshold to catch more eager reclaim candidates.