RFR: 8280994: [XWayland] Drag and Drop does not work in java -> wayland app direction [v3]

[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.

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

  review comments.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14266/files
  - new: https://git.openjdk.org/jdk/pull/14266/files/ec4493f5..c0b43f19

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14266&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14266&range=01-02

  Stats: 13 lines in 2 files changed: 5 ins; 2 del; 6 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