RFR: 6507: Use GraphViz to render stack traces [v4]

[Marcus Hirt]

> Still need some pruning options to not be insanely slow when having plenty of nodes, but this is a start.

Marcus Hirt has updated the pull request incrementally with one additional commit since the last revision:

  Fixing review issues

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Changes:
  - all: https://git.openjdk.java.net/jmc/pull/162/files
  - new: https://git.openjdk.java.net/jmc/pull/162/files/469f8d93..a3d0872c

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jmc&pr=162&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jmc&pr=162&range=02-03

  Stats: 13 lines in 3 files changed: 12 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jmc/pull/162.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/162/head:pull/162

PR: https://git.openjdk.java.net/jmc/pull/162