[jdk8u-dev] RFR: 8296632: Write a test to verify the content change of TextArea sends TextEvent

[Victor Rudometov]

Backport for [JDK-8296632](https://bugs.openjdk.org/browse/JDK-8296632) Write a test to verify the content change of TextArea sends TextEvent 

Clean Backport.
New test, low risk.
Test passes during manual run on linux and mac.

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Commit messages:
 - Backport 14592778b19af792f7394be381c3e23bf216372d

Changes: https://git.openjdk.org/jdk8u-dev/pull/198/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=198&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/jdk8u-dev/pull/198.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u-dev pull/198/head:pull/198

PR: https://git.openjdk.org/jdk8u-dev/pull/198