RFR: 8257602: Introduce JFR Event Throttling and new jdk.ObjectAllocationSample event (enabled by default) [v4]

[Markus Grönlund]

> Greetings,
> 
> please help review this enhancement to let JFR sample object allocations by default.
> 
> A description is provided in the JIRA issue.
> 
> Thanks
> Markus

Markus Grönlund has updated the pull request incrementally with 12 additional commits since the last revision:

 - initialization check
 - thread locals and detach and reattach
 - Tighter ThrottleUnit
 - JFC control elements
 - TLAB include
 - ThrottleUnit enum
 - remote tests
 - jfc control attributes
 - Sampling frequency adjustment for large objects
 - Treat large objects as tlabs for sampling purposes
 - ... and 2 more: https://git.openjdk.java.net/jdk/compare/6918f0c8...4e986552

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1624/files
  - new: https://git.openjdk.java.net/jdk/pull/1624/files/6918f0c8..4e986552

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1624&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1624&range=02-03

  Stats: 530 lines in 13 files changed: 174 ins; 285 del; 71 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1624.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1624/head:pull/1624

PR: https://git.openjdk.java.net/jdk/pull/1624