RFR: CODETOOLS-7903560: JMH: async profiler reports only the last fork result

[Jonas Konrad]

Without this change, async-profiler would write the same result in each fork, overwriting the previous result.

This patch introduces a new "FileResult" class that collects the output paths of each benchmark. In `afterTrial`, the output files are moved to a new path that includes the pid (fork number would be an alternative but it's not as easily available).

At the moment, results of different runs are not coalesced. But with these changes, it would be easy to coalesce at least the results of the "collapsed" output mode. I plan to do this in another PR.

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Commit messages:
 - Merge branch 'master' into async-fork
 - license headers
 - Include PID in async-profiler file name when forking

Changes: https://git.openjdk.org/jmh/pull/121/files
 Webrev: https://webrevs.openjdk.org/?repo=jmh&pr=121&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903560
  Stats: 333 lines in 3 files changed: 306 ins; 12 del; 15 mod
  Patch: https://git.openjdk.org/jmh/pull/121.diff
  Fetch: git fetch https://git.openjdk.org/jmh.git pull/121/head:pull/121

PR: https://git.openjdk.org/jmh/pull/121