RFR: 8280994: [XWayland] Drag and Drop does not work in java -> wayland app direction

[Alexander Zvegintsev]

This change resolves the issue that drag and drop from a Java application to a native Wayland application (such as gedit) is not possible on Linux.

Our code it quite picky for the drop target, and requires it to be a top level window with the WM_STATE property set, whereas the XWayland server provides dummy windows without this property.
So now we make an exclusion for this case.

After the fix it successfully passes previously failed related manual jtreg/conformance tests on Wayland.
Other tests are also passed.

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Commit messages:
 - typo
 - initial

Changes: https://git.openjdk.org/jdk/pull/14266/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14266&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8280994
  Stats: 41 lines in 1 file changed: 40 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/14266.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14266/head:pull/14266

PR: https://git.openjdk.org/jdk/pull/14266