RFR: 8306575: Clean up and open source four Dialog related tests [v2]

[Alexander Zuev]

> Cleaned up and stabilized four Dialog-related tests.

Alexander Zuev has updated the pull request incrementally with one additional commit since the last revision:

  Added couple of empty lines to make code nore readable.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/13592/files
  - new: https://git.openjdk.org/jdk/pull/13592/files/233bc71b..de12275d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13592&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13592&range=00-01

  Stats: 2 lines in 2 files changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/13592.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13592/head:pull/13592

PR: https://git.openjdk.org/jdk/pull/13592