RFR: 8296632: Write a test to verify the content change of TextArea sends TextEvent.

[ravi gupta]

This testcase Verify the content changes of a TextArea for the following assertions.

a. TextListener get invoked when the content of a TextArea gets changed.
b. TextListener not get invoked during text selection or when Special keys such as Function Keys are pressed.


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

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Commit messages:
 - 8296632: Write a test to verify the content change of TextArea sends TextEvent.

Changes: https://git.openjdk.org/jdk/pull/11052/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11052&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296632
  Stats: 141 lines in 1 file changed: 141 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/11052.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11052/head:pull/11052

PR: https://git.openjdk.org/jdk/pull/11052