[jdk11u-dev] RFR: 8306681: Open source more AWT DnD related tests

[Andrew Lu]

I backport this for parity with 11.0.24-oracle.

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Commit messages:
 - Backport 05af487a2d9b85b87d13ea23776d04e52c67bf49

Changes: https://git.openjdk.org/jdk11u-dev/pull/2526/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2526&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306681
  Stats: 544 lines in 7 files changed: 544 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2526.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2526/head:pull/2526

PR: https://git.openjdk.org/jdk11u-dev/pull/2526