Merge "Mark as stable and add API docs for dalvik.system.VMDebug" am: 59688d38d1 am: 76ae1365b1 am: 6af8345fec

Original change: https://android-review.googlesource.com/c/platform/libcore/+/1584809

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: Idec3023d8c92031892d6b2e0d5b1082a30014bb9