Add macOS device runner support

[velocitysystems]

Description of Change

Add macOS device runner support for xunit.
Requires Visual Studio for Mac to run the test.xunit.runner.macOS project.

Issues Resolved

• Device runner for macOS? #75

Platforms Affected

macOS

[clairernovotny]

Hi,

I appreciate adding support for macOS, but it has to be done in a way that's compatible with everything else here. It should not need a separate project. Visual Studio for Windows should be able to build Xamarin.Mac20 projects, and they can be multi-targeted.

I would suggest adding a Xamarin.Mac20 target to the xunit.runner.devices project, then make whatever changes are required there. There should be a new "head" project to test it. That head project can likely be only run from macOS, though it should build from Windows.

Thanks!

[velocitysystems]

@onovotny Thanks Oren. I'm working on this right now. I've updated the Unit.Runner.Devices project file to build a "xamarinmac20" target and now just adding the test project and template.

[velocitysystems]

@onovotny Oren, I've added in the test.xunit.runner.macOS project (which builds on Windows).
Please have a look and let me know if you have any feedback. I'll work on adding the project template on Monday.