RFR: 8148041: Test java/awt/Mouse/TitleBarDoubleClick/TitleBarDoubleClick fails on Ubuntu with mouseReleased event after double click on title bar

[Alexander Zvegintsev]

This test was problem listed with ["some tests that leave windows open on the desktop" reason](https://github.com/openjdk/jdk/commit/fd8df3adf13f5df8f5f95482b8e0a70bc519f39f)

The main issue with the test is that it may pass, but in fact the actual test was not even performed. <br>`jtreg` kills the test window after exiting main and ends the test before it double clicks on window's title(actual test starts from `windowActivated` event).

So the test was refactored and stabilized:
* robot invocation moved from EDT to main thread.
* throwing test exception is performed only after frame is disposed
* extra delay added after showing window.

Old Ubuntu 16.04 and macOS 10.10.5 failures is no longer reproducible on modern systems.

CI testing looks good.

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

Commit messages:
 - refactor
 - clean up

Changes: https://git.openjdk.org/jdk/pull/11150/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11150&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8148041
  Stats: 71 lines in 2 files changed: 19 ins; 8 del; 44 mod
  Patch: https://git.openjdk.org/jdk/pull/11150.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11150/head:pull/11150

PR: https://git.openjdk.org/jdk/pull/11150