RFR: 8365611: Throttle any JFR event

[Thomas Stuefe]

This patch prepares the way to throttle any JFR event, not only the three events for which we hard-code throttlers. It also cleans up the throttler code and replaces the switch construct with a lookup table.

The patch does not yet enable throttling for any other event. I can do that, if we agree that this is okay. But I'd like to avoid arguments, so for now the patch does not add the ability to throttle to any event; it just makes it trivially easy to do that if needed.

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Commit messages:
 - Update jfrEventThrottler.cpp
 - wip
 - fixes
 - start

Changes: https://git.openjdk.org/jdk/pull/26801/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26801&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8365611
  Stats: 84 lines in 2 files changed: 42 ins; 22 del; 20 mod
  Patch: https://git.openjdk.org/jdk/pull/26801.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26801/head:pull/26801

PR: https://git.openjdk.org/jdk/pull/26801