RFR: 6669: FlameGraphView tree calculation should (probably) be interruptable [v6]

[Miroslav Wengner]

> fix to bug: https://bugs.openjdk.java.net/browse/JMC-6669

Miroslav Wengner has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains ten additional commits since the last revision:

 - 6669: typo correction
 - 6669: only last thread, cleaned
 - Merge branch 'master' of https://github.com/openjdk/jmc into bugfix/6669_FlameGraphView_tree_calculation_should_probably_be_interruptable
 - 6669: correction
 - 6669: spotless needs
 - 6669: more executor threads,runnable, canceling threads, cleanup
 - 6669: correction
 - 6669: spotless needs
 - 6669: model calculation cancelation

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Changes:
  - all: https://git.openjdk.java.net/jmc/pull/135/files
  - new: https://git.openjdk.java.net/jmc/pull/135/files/a9bcda0e..3bba252f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jmc&pr=135&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jmc&pr=135&range=04-05

  Stats: 106 lines in 2 files changed: 46 ins; 47 del; 13 mod
  Patch: https://git.openjdk.java.net/jmc/pull/135.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/135/head:pull/135

PR: https://git.openjdk.java.net/jmc/pull/135