[jdk11u-dev] RFR: 8297489: Modify TextAreaTextEventTest.java as to verify the content change of TextComponent sends TextEvent

[Goetz Lindenmaier]

I backport this for parity with 11.0.19-oracle.

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Commit messages:
 - Backport 7d20a60a983e459ea1c4e843fbde70fb796c6249

Changes: https://git.openjdk.org/jdk11u-dev/pull/1715/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1715&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297489
  Stats: 302 lines in 2 files changed: 161 ins; 141 del; 0 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1715.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev pull/1715/head:pull/1715

PR: https://git.openjdk.org/jdk11u-dev/pull/1715