* [tests] Minor refactor to get better Xcode version parsing.
* Rename Configuration.XcodeVersion to XcodeVersionString.
* Add Configuration.XcodeVersion a parsed Version instane of XcodeString.
* [tests] Ignore all 'MT0099: Not linking with WatchKit because Xcode 11 beta 1' warnings in tests.
* [tests] Adjust min OS version tests for Xcode 11b1.
* [tests] Adjust tests for changes in 'nm' output.
* [tests] Adjust tests for name changes in Clang.
* [tests] Adjust tests for changes in ld warning format.
* [msbuild] 'metal' and 'metallib' aren't in PATH anymore, so use xcrun to execute them.
* [msbuild] Fix DevicePlatformBinDir for the Metal and MetalLib targets on iOS.
Also set the SDKROOT variable, otherwise metal and metallib don't work
properly, and revert the previous attempt at a fix (use xcrun).
* [tests] Simplify version parsing code to not version parse anymore.
* [tests] Add FIXME for once Apple fixes the WatchKit disappearance.
- Fixes#4576: [xcode10] 'Metal Game' fails to build. (https://github.com/xamarin/xamarin-macios/issues/4576)
In Xcode 10 Apple moved the "metal" binary from `/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/usr/bin/metal` to `/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/metal`.