RFR: JDK-8307128: Open source some drag and drop tests 4

[Alisen Chung]

added DnD tests

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Commit messages:
 - added dnd tests

Changes: https://git.openjdk.org/jdk/pull/13765/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13765&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8307128
  Stats: 1678 lines in 5 files changed: 1678 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/13765.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13765/head:pull/13765

PR: https://git.openjdk.org/jdk/pull/13765