8156500: Move Reference pending list into VM to prevent deadlocks
Summary: Move reference pending list and locking into VM
Reviewed-by: coleenp, dholmes, dcubed, mchung, plevart
Contributed-by: kim.barrett@oracle.com, per.liden@oracle.com

8151601: Cleanup locking of the Reference pending list
Reviewed-by: brutisso, stefank

8067194: Restructure hotspot/agent/src to conform the modular source layout
Summary: Move sources under jdk.hotspot.agent
Reviewed-by: ihse, erikj, jbachorik