RFR: 8295651: JFR: 'jfr scrub' should summarize what was removed

[Erik Gahlin]

Could I have a review of an enhancement that summarizes the results of `jfr scrub`?

To accommodate this feature, I made some additional changes:

- Added a LongMap::values() method.
- Added a Command::printf(...) method, which is now also used by `jfr summary`.
- Improved TestScrub.java so it now creates a file that spans multiple chunks, including an empty one.

See issue for example output.

Testing: jdk/jdk/jfr

Thanks
Erik

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Commit messages:
 - Only collect if 'jfr scrub' is used
 - Initial

Changes: https://git.openjdk.org/jdk/pull/24669/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24669&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295651
  Stats: 138 lines in 9 files changed: 123 ins; 2 del; 13 mod
  Patch: https://git.openjdk.org/jdk/pull/24669.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24669/head:pull/24669

PR: https://git.openjdk.org/jdk/pull/24669