RFR: 8310994: Add JFR event for selection operations

[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

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Commit messages:
 - remove trailing whitespace
 - event logic outside of the lock, selector in try block
 - remove unused import
 - fix TestConfigure failure
 - add event defaults
 - Merge branch 'master' into JDK-8310994
 - minor test cleanup
 - Merge branch 'master' into JDK-8310994
 - 8310994: Add JFR event for selection operations

Changes: https://git.openjdk.org/jdk/pull/16710/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16710&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8310994
  Stats: 265 lines in 9 files changed: 264 ins; 0 del; 1 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