[8u] RFR: 8226806: [macOS 10.14] Methods of Java Robot should be called from appropriate thread

[Vladimir Kempik]

Hello
Please review this backport of 8226806.
It wasn’t applying cleanly due to context code changes, also smart part of newer testlibrary were needed.
Since the support for xcode12 were approved ( see JDK-8267545 ), it becomes important to backport some of the bug fixes as well.
This fix passed all the testing in zulu8 for past 3 releases ( since October 2020)

The webrev doesn’t reflect white space changes in CRobot.m, so the patch looks smaller than original.

The webrev: http://cr.openjdk.java.net/~vkempik/8226806/webrev.01/
The bug: https://bugs.openjdk.java.net/browse/JDK-8226806
The orignal patch: https://hg.openjdk.java.net/jdk/jdk/rev/23dc143cca50 <https://hg.openjdk.java.net/jdk/jdk/rev/23dc143cca50>

Thanks in advance, Vladimir.