jfx-tests repo: JemmyFX test suite

[Kevin Rushforth]

As part of an effort to increase test coverage of JavaFX, particularity 
in the graphics area, we are reviving the JemmyFX test suite that was 
hosted in the Mercurial jfx-dev/tests repo [1]. To that end, we have 
converted the tests repo to git (using the Skara tooling), and made it 
available on GitHub [2].

A PR will be raised soon to integrate JDK-8315409 [3] to get it running 
again, although it's not yet ready for general use, since there is still 
a fair bit of work to do.

Our primary motivation for spending time on this now is to help us test 
the Metal graphics pipeline that is currently being developed in the 
metal branch of jfx-sandbox [4], but it might also be able to provide an 
additional level of testing in general for scenegraph, graphics 
(including some limited 3D), and controls.

-- Kevin

[1] https://hg.openjdk.org/openjfx/jfx-dev/tests
[2] https://github.com/openjdk/jfx-tests
[3] https://bugs.openjdk.org/browse/JDK-8315409
[4] https://github.com/openjdk/jfx-sandbox/tree/metal