[xbuild] Implement GetDirectoryNameOfFileAbove ()

The method looks for the given file starting at the given path and traverses
the directory tree up until the file is found or root is reached.
Respond to code review feedback
Respond to code review feedback
Merge pull request #1465 from akoeplinger/msbuild-getdirnameoffileabove

[xbuild] Implement GetDirectoryNameOfFileAbove ()