<AWT Dev> RFR: 8225790: Two NestedDialogs tests fail on Ubuntu

[Pankaj Bansal]

Two NestedDialog tests are failing on Ubuntu 20.04 intermittently. I am able to reproduce the issue locally also
sometime.

Tests are creating a frame and then create multiple dialogs. These tests are using classes VisibilityValidator and
Waypoint (present in test/jdk/java/awt/regtesthelpers) for doing basic operations like waiting for a Frame/Dialog to
become visible, doing a mouse click on a Frame/Window. Also, the test is not using Robot waitForIdle properly. so
making the test less stable.

I have removed the lot of unnecessary code from the tests. Also, I have added proper AutoDelay on Robot and used
waitForIdel properly. I have also removed the class VisibilityValidator and Waypoint. These classes were added with in
test/jdk/java/awt/regtesthelpers when these tests were added. I don't see any use of these classes. No other test is
using these classes at all and there is too much code in these classes.

I have run the multiple iterations of the test on mach5, it passes successfully. I have also run a full job to make
confirm VisibilityValidator and Waypoint are not being used anywhere else.

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Commit messages:
 - 8225790: Two NestedDialogs tests fail on Ubuntu

Changes: https://git.openjdk.java.net/jdk/pull/721/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=721&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8225790
  Stats: 788 lines in 4 files changed: 81 ins; 610 del; 97 mod
  Patch: https://git.openjdk.java.net/jdk/pull/721.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/721/head:pull/721

PR: https://git.openjdk.java.net/jdk/pull/721