Robot capture tests fail intermittently on Mac M1

When running the full test suite, including robot tests on an M1 MacBook Pro, we get a few failures in screen capture test. It looks like the failures are caused by the cursor being in the area that is being read using the robot screen capture APIs (suggesting that the cursor is captured, which seems odd).

The following tests fail:

RobotTest > testScreenCapture FAILED
RegionBackgroundImageUITest > alignedImage_RoundSpace FAILED
RegionBackgroundImageUITest > unalignedImage_PositionCenterBottom FAILED
RegionBackgroundImageUITest > alignedImage_PositionBottomRightRepeatX FAILED
RegionBackgroundImageUITest > unalignedImage_PositionCenterTop FAILED
RegionBackgroundImageUITest > alignedImage FAILED
RegionBackgroundImageUITest > unalignedImage_RepeatX FAILED
RegionBackgroundImageUITest > alignedImage_PositionCenterLeftRepeatX FAILED
RegionBackgroundImageUITest > alignedImage_PositionCenterRightRepeatX FAILED
RegionBackgroundImageUITest > alignedImage_RepeatX FAILED
RegionBackgroundImageUITest > alignedImage_PositionCenterFiftyPercentRepeatX FAILED
RegionBackgroundImageUITest > alignedImage_PositionCenterRepeatX FAILED
RegionBackgroundImageUITest > unalignedImage_PositionCenterTopRepeatX FAILED
RegionBackgroundImageUITest > unalignedImage_PositionCenterLeftRepeatX FAILED
RegionBackgroundImageUITest > alignedImage_PositionCenterFiftyPercent FAILED
RegionBackgroundImageUITest > alignedImage_PositionCenter FAILED
RegionBackgroundImageUITest > unalignedImage_PositionCenterBottomRepeatX FAILED
RegionBackgroundImageUITest > alignedImage_Round FAILED
RegionBackgroundImageUITest > alignedImage_Space FAILED
RegionBackgroundImageUITest > alignedImage_PositionCenterTopRepeatX FAILED
RegionBackgroundImageUITest > alignedImage_PositionCenterTopRepeatY FAILED
RegionBackgroundImageUITest > alignedImage_PositionCenterBottom FAILED
RegionBackgroundImageUITest > unalignedImage_PositionBottomRightRepeatX FAILED
RegionBackgroundImageUITest > alignedImage_PositionCenterBottomRepeatX FAILED
RegionBackgroundImageUITest > alignedImage_PositionCenterBottomRepeatY FAILED
RegionBackgroundImageUITest > alignedImage_PositionCenterTop FAILED


If I run just the RegionBackgroundImageUITest it passes. If I manually move the mouse out of the way after running a test that laves the cursor in the "wrong" place before the RegionBackgroundImageUITest run, then it passes.

That isn't possible for RobotTest, since other tests in the same class move the mouse.

The proposed fix is to call mouseMove(0, 0) in an `@Before` method of all tests that do screen capture. Further, the RobotTest should create it's initial Stage with a Scene so that it doesn't end up at (0,0) which can cause other problems.