RFR: 8310994: Add JFR event for selection operations [v4]

[Tim Prinzing]

> Added mirror event with static methods: jdk.internal.event.SelectionEvent that provides the duration of select calls and the count of how many keys are available.
> 
> Emit the event from SelectorImpl::lockAndDoSelect
> 
> Test at jdk.jfr.event.io.TestSelectionEvents

Tim Prinzing has updated the pull request incrementally with one additional commit since the last revision:

  comment fixup

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/16710/files
  - new: https://git.openjdk.org/jdk/pull/16710/files/13262293..18064cd1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16710&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16710&range=02-03

  Stats: 3 lines in 1 file changed: 0 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/16710.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16710/head:pull/16710

PR: https://git.openjdk.org/jdk/pull/16710