RFR: 8337827: [XWayland] Skip failing tests on Wayland

[Alexander Zvegintsev]

This changeset introduces the `Util.isOnWayland()` method and skips failing tests on Wayland.

After that, all tests run on Wayland without failures.

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Commit messages:
 - add javadoc
 - 8337827: [XWayland] Skip failing tests on Wayland

Changes: https://git.openjdk.org/jfx/pull/1536/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1536&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8337827
  Stats: 31 lines in 4 files changed: 25 ins; 5 del; 1 mod
  Patch: https://git.openjdk.org/jfx/pull/1536.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1536/head:pull/1536

PR: https://git.openjdk.org/jfx/pull/1536