[15u] RFR (S) 8249192: MonitorInfo stores raw oops across safepoints

[Aleksey Shipilev]

Original bug:
   https://bugs.openjdk.java.net/browse/JDK-8249192
   https://hg.openjdk.java.net/jdk/jdk/rev/61f9028f360d

15u variant:
   https://cr.openjdk.java.net/~shade/8249192/webrev.15u.01/

It differs from jdk/jdk variant by a conflict in jvmtiEnvBase.cpp, where removed "ResourceMark rm" 
does not have "current_thread" argument yet. It was added later with JDK-8247729:
   https://hg.openjdk.java.net/jdk/jdk/rev/f8a9be0f9e1a#l2.82

Testing: tier{1,2} with and without Shenandoah [which seems to find some of these bugs]

-- 
Thanks,
-Aleksey