Backport JDK-8037914 (JFR event for string deduplication) to sapmachine21

[parttimenerd]

Backport the new jdk.StringDeduplication JFR event to sapmachine21.

Upstream:

JDK-8037914 "Add JFR event for string deduplication" (https://github.com/SAP/SapMachine/commit/3a2845f334a59670d54699919073f0e908c038c4)
JDK-8372348 "Adjust some UL / JFR string deduplication output messages" (https://github.com/SAP/SapMachine/commit/3f20eb943532c5c76e55b14292139749bd704ce4)

The event exposes per-cycle concurrent string-deduplication statistics (inspected/known/shared/new/deduplicated counts and bytes, skipped dead/incomplete/shared, and processing/table-resize/table-cleanup timings) under category "Java Virtual Machine, GC, Detailed". This enables consuming string-dedup metrics via JFR instead of only -Xlog:stringdedup.