RFR: 8037914: Add JFR event for string deduplication [v2]

[Francesco Andreuzzi]

> In this PR I introduce two new JFR events:
> - `jdk.StringDeduplicationStatistics`
> - `jdk.StringDeduplicationTimes`
> 
> The events are emitted every time a deduplication cycle happens, and they contain information about that cycle only.
> 
> Passes tier1 and tier2 (fastdebug).

Francesco Andreuzzi has updated the pull request incrementally with one additional commit since the last revision:

  one event

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Changes:
  - all: https://git.openjdk.org/jdk/pull/28015/files
  - new: https://git.openjdk.org/jdk/pull/28015/files/1cb7d996..bff0fd30

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28015&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28015&range=00-01

  Stats: 61 lines in 8 files changed: 8 ins; 52 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/28015.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28015/head:pull/28015

PR: https://git.openjdk.org/jdk/pull/28015