RFR: 8299296: Write a test to verify the components selection sends ItemEvent

[Ravi Gupta]

This testcase verifies the following assertions

a. Selecting an item in the Choice using mouse generates ItemEvent.
b. Single-click on an Checkbox generates ItemEvent.

Testing:
Tested using Mach5(20 times per platform) in macos, linux and windows and got all pass.

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Commit messages:
 - Write a test to verify the components selection sends ItemEvent

Changes: https://git.openjdk.org/jdk/pull/11786/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11786&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8299296
  Stats: 123 lines in 1 file changed: 123 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/11786.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11786/head:pull/11786

PR: https://git.openjdk.org/jdk/pull/11786