RFR: 8037914: Add JFR event for string deduplication [v6]

[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 incrementally with one additional commit since the last revision:

  rename. start/end time

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/28015/files
  - new: https://git.openjdk.org/jdk/pull/28015/files/3793befd..090c02bc

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28015&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28015&range=04-05

  Stats: 12 lines in 6 files changed: 5 ins; 0 del; 7 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