RFR: 8213120: java/awt/TextArea/AutoScrollOnSelectAndAppend/AutoScrollOnSelectAndAppend.java fails on mac10.13

[Jayathirth D V]

Looks like this test was failing in one local system in JDK12 and it was problemlisted.
I ran this test multiple times in our CI systems it doesnt fail.
Made modifications to move test window to the middle of the screen and added autodelay for robot. Tested in our CI systems with modifications and test run is green.

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Commit messages:
 - 8213120: java/awt/TextArea/AutoScrollOnSelectAndAppend/AutoScrollOnSelectAndAppend.java fails on mac10.13

Changes: https://git.openjdk.java.net/jdk/pull/6116/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6116&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8213120
  Stats: 3 lines in 2 files changed: 2 ins; 1 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6116.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6116/head:pull/6116

PR: https://git.openjdk.java.net/jdk/pull/6116