RFR: 8037914: Add JFR event for string deduplication [v7]

[Francesco Andreuzzi]

> In this PR I introduce a new JFR event: `jdk.StringDeduplication`
> 
> The new event is emitted every time a deduplication cycle happens.
> 
> Passes tier1 and tier2 (fastdebug).

Francesco Andreuzzi has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 15 additional commits since the last revision:

 - remove elapsed. remove idle
 - Merge branch 'master' into JDK-8037914
 - rename. start/end time
 - no start
 - enable
 - bytes to size
 - disable
 - revert
 - one event
 - trailing
 - ... and 5 more: https://git.openjdk.org/jdk/compare/84b50801...fc47a64e

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/28015/files
  - new: https://git.openjdk.org/jdk/pull/28015/files/090c02bc..fc47a64e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28015&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28015&range=05-06

  Stats: 242359 lines in 1920 files changed: 155343 ins; 52311 del; 34705 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