RFR/RFA (M): 8185003: JMX: Add a version of ThreadMXBean.dumpAllThreads with a maxDepth argument

[Hohensee, Paul]

Please review this backport to jdk8u. I especially need a CSR review, since the CSR approval process can be a bottleneck. The patch significantly reduces fleet profiling overhead, and a version of it has been in production at Amazon for over 3 years.

Original JBS issue: https://bugs.openjdk.java.net/browse/JDK-8185003
Original CSR: https://bugs.openjdk.java.net/browse/JDK-8185705
Original patch: http://hg.openjdk.java.net/jdk10/master/rev/68d46cb9be45

Backport JBS issue: https://bugs.openjdk.java.net/browse/JDK-8251494
Backport CSR: https://bugs.openjdk.java.net/browse/JDK-8251498
Backport JDK webrev: http://cr.openjdk.java.net/~phh/8185003/webrev.8u.jdk.05/
Backport Hotspot webrev: http://cr.openjdk.java.net/~phh/8185003/webrev.8u.hotspot.05/

Details of the interface changes needed for the backport are in the Description of the Backport CSR 8251498. The actual functional changes are minimal and low risk.

Passes the included (suitably modified) test, as well as the tests in

jdk/test/java/lang/management/ThreadMXBean
jdk/test/com/sun/management/ThreadMXBean

Thanks,
Paul