Revert "Revert "Add concurrent card graying for immune spaces""

Added an additional checkpoint before the concurrent graying to set
the mark entrypoints to non-null.

Bug: 37876887

Test: test-art-host

This reverts commit c83dd7bfde2171c879efb92a31a363505385ffb9.

Change-Id: I961c4631c9595c52cd7765f61b22b8291fef2088
14 files changed