RFR: 8340790: Open source several AWT Dialog tests - Batch 4

[Tejesh R]

Open source these AWT Dialog tests:

java/awt/Dialog/FileDialogGetFileTest.java
java/awt/Dialog/EnabledResetTest.java
java/awt/Dialog/ChoiceModalDialogTest.java
java/awt/Dialog/DialogBackgroundTest.java

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Commit messages:
 - Open source

Changes: https://git.openjdk.org/jdk/pull/21404/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21404&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340790
  Stats: 515 lines in 4 files changed: 515 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/21404.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21404/head:pull/21404

PR: https://git.openjdk.org/jdk/pull/21404