[jdk11u-dev] RFR: 8307128: Open source some drag and drop tests 4

[luchenlin]

I backport this for parity with 11.0.21-oracle.
test/jdk/java/awt/dnd/MouseExitGestureTriggerTest.java
add backport for [JDK-8307799](https://bugs.openjdk.org/browse/JDK-8307799), Without this fix test will fail.
other backport clean.

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Commit messages:
 - Backport 98294242a94c611e2a713c2d520e59dd873ae4a0

Changes: https://git.openjdk.org/jdk11u-dev/pull/2060/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2060&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8307128
  Stats: 1680 lines in 5 files changed: 1680 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2060.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2060/head:pull/2060

PR: https://git.openjdk.org/jdk11u-dev/pull/2060