[Core] Handle $(CONFIGURATION) and $(PLATFORM) in OutputDirectory

These placeholders need to be replaced so the full (correct) path
can be obtained inside monodevelop.

We will need to review everywhere we directly use 'IntermediateOutputDirectory' and 'OutputDirectory' to either leave them as-is (if they need the raw version) or port them to use the Evaluated* versions if they need the processed version of the path.

Added test covering the change.