RFR: 8328697: SubMenuShowTest and SwallowKeyEvents tests stabilization [v2]

[Alexander Zvegintsev]

> Two tests may fail intermittently on Wayland, the standard `waitForIdle` and `delay` fixes the issue.
> 
> Manual and CI testing looks good.

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

  author removed, ../../../regtesthelpers -> /java/awt/regtesthelpers, moved whole block closer to class declaration

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Changes:
  - all: https://git.openjdk.org/jdk/pull/18431/files
  - new: https://git.openjdk.org/jdk/pull/18431/files/ef599122..3c18826e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18431&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18431&range=00-01

  Stats: 51 lines in 2 files changed: 24 ins; 27 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/18431.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18431/head:pull/18431

PR: https://git.openjdk.org/jdk/pull/18431