[11u] RFR: 8257602: Introduce JFR Event Throttling and new jdk.ObjectAllocationSample event (enabled by default)

[Jaroslav Bachorík]

Greetings,

I would like to ask for review of this JDK11u backport patch:

Issue   :  https://bugs.openjdk.java.net/browse/JDK-8257602
Webrev: http://cr.openjdk.java.net/~jbachorik/8257602/jdk11/00/webrev/

The webrev contains the main change backported from JDK-8257602 and
the followup patch for AIX build failure resolved as JDK-8258094. I
decided to roll both changesets into one webrev to get a fully
buildable system once this backport request is approved.

The original changeset of JDK-8257602 had to be slightly adjusted for
the following:
* hunk offsets not matching because of larger structural changes
   resolution: the appropriate code was inserted manually
* missing Atomic::load_acquire and Atomic::release_store functions
   resolution: used OrderAccess::* equivalents
* different argument order for Atomic::cmpxchg and Atomic::store
   resolution: modified the call-site argument order to match what is
provided by Atomic::*
* [test] missing support for event streaming
   resolution: used the recording in non-streaming mode while keeping
the test semantics

All tier1, tier2 and jdk_jfr tests are passing with the changes applied.

Cheers,

-JB-