RFR: 8196018: java/awt/Scrollbar/ScrollbarMouseWheelTest/ScrollbarMouseWheelTest.java fails

[Alexander Zvegintsev]

The issue contains evaluation that:
* the test is not failing on Windows
* it also fails on Linux(but provided stack trace with failure is from different test)

I rechecked the test and it does not fail on all platforms.

Test is stabilized:
* replaced synchronization on windowActivated event with standard `robot.waitForIdle(); robot.delay(1000);`
* Robot autoDelay decreased to 250 to make the test go faster. It it still a reasonable value.

CI testing looks good also.

-------------

Commit messages:
 - stabilize
 - clean up

Changes: https://git.openjdk.org/jdk/pull/11213/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11213&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8196018
  Stats: 51 lines in 2 files changed: 15 ins; 28 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/11213.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11213/head:pull/11213

PR: https://git.openjdk.org/jdk/pull/11213