[jdk11u-dev] RFR: 8316154: Opensource JTextArea manual tests

[Amos Shi]

Backport of [JDK-8316154](https://bugs.openjdk.org/browse/JDK-8316154)

Testing
- Local: Test passed
  - `bug4265784.java`: Test results: passed: 1
- Pipeline: 
- Testing Machine:

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Commit messages:
 - Backport 33c62e4fffe33a7593fd0c01de53507bfd01dc3b

Changes: https://git.openjdk.org/jdk11u-dev/pull/2660/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2660&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316154
  Stats: 90 lines in 1 file changed: 90 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2660.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2660/head:pull/2660

PR: https://git.openjdk.org/jdk11u-dev/pull/2660