RFR: 7903324: Improve per-class reporting of JUnit tests, in .jtr file [v2]

[Christian Stein]

> Improve per-class reporting of JUnit tests by using a custom `TestExecutionListener` in `JUnitRunner`.

Christian Stein has updated the pull request incrementally with one additional commit since the last revision:

  More comments addressed

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Changes:
  - all: https://git.openjdk.org/jtreg/pull/127/files
  - new: https://git.openjdk.org/jtreg/pull/127/files/da0cafe2..148dc5d3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jtreg&pr=127&range=01
 - incr: https://webrevs.openjdk.org/?repo=jtreg&pr=127&range=00-01

  Stats: 63 lines in 2 files changed: 46 ins; 13 del; 4 mod
  Patch: https://git.openjdk.org/jtreg/pull/127.diff
  Fetch: git fetch https://git.openjdk.org/jtreg pull/127/head:pull/127

PR: https://git.openjdk.org/jtreg/pull/127