RFR: 8306943: Open source several dnd AWT tests

[Alexander Zvegintsev]

Open sourcing few more tests:

java/awt/dnd/DnDAWTLockTest/DnDAWTLockTest.java
java/awt/dnd/DragGestureInvokeLaterTest/DragGestureInvokeLaterTest.java
java/awt/dnd/DragOverDropTargetPerformanceTest/DragOverDropTargetPerformanceTest.java
java/awt/dnd/DragSourceDragEventModifiersTest/DragSourceDragEventModifiersTest.java
java/awt/dnd/DragSourceGCrashTest/DragSourceGCrashTest.java


Testing looks good.

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Commit messages:
 - initial

Changes: https://git.openjdk.org/jdk/pull/13752/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13752&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306943
  Stats: 1349 lines in 5 files changed: 1349 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/13752.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13752/head:pull/13752

PR: https://git.openjdk.org/jdk/pull/13752