RFR: 6905: Add rule for heap dumps [v3]

[Jean-Philippe Bempel]

> Rule based on ne JDK15 jdk.HeapDump event.
> If at least on heap dump is performed, rule indicates it as information, score 50.
> For test added a new JFR file containing an example where 2 dumps were performed

Jean-Philippe Bempel has updated the pull request incrementally with one additional commit since the last revision:

  fix formatting

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Changes:
  - all: https://git.openjdk.java.net/jmc/pull/113/files
  - new: https://git.openjdk.java.net/jmc/pull/113/files/3a0eb713..821404c0

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jmc&pr=113&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jmc&pr=113&range=01-02

  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jmc/pull/113.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/113/head:pull/113

PR: https://git.openjdk.java.net/jmc/pull/113