RFR: 8372348: Adjust some UL / JFR string deduplication output messages

[Matthias Baesken]

There is some UL output in the string deduplication code that is not very clear and has room for improvement.
The inspected strings number should be shown and the new unknown strings get a changed text.
(also the new JFR strip dedup event  description is slightly adjusted)

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Commit messages:
 - JDK-8372348

Changes: https://git.openjdk.org/jdk/pull/28455/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28455&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8372348
  Stats: 13 lines in 2 files changed: 2 ins; 0 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/28455.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28455/head:pull/28455

PR: https://git.openjdk.org/jdk/pull/28455