[9] Review request for 8171952: [macosx] AWT_Modality/Automated/ModalExclusion/NoExclusion/ModelessDialog test fails as DummyButton on Dialog did not gain focus when clicked.

[Dmitry Markov]

Hello,

Could you review a fix for jdk9, please?

        bug: https://bugs.openjdk.java.net/browse/JDK-8171952
        webrev: http://cr.openjdk.java.net/~dmarkov/8171952/webrev.00/

Problem description:
LWCToolkit.getPlatformWindowUnderMouse() looks for a window only at normal 
window level/layer, (i.e. NSNormalWindowLevel). However after integration of 
JDK-8080729 the child windows of focused window are placed to floating level, 
(i.e. NSFloatingWindowLevel).
So the following situation may take place: the window is in focused state and 
obscured by its child dialog, but the current implementation of 
getPlatformWindowUnderMouse() reports that the window is under mouse.

Fix:
getPlatformWindowUnderMouse() should look at all possible window levels/layers 
during retrieval of the topmost window under mouse.

Thanks,
Dmitry