Show warning/info at compile time when [DeploymentItem] attribute used for .NetCore or UWP project

[jayaranigarg]

Description

Currently user have no way to figure out that [DeploymentItem] is not supported for UWP/.Net Core projects. Adding a meaningful warning/information message at compile time can save both of our time and developer's time.

Steps to reproduce

1. Create a UWP test project.
2. Add [DeploymentItem] attribute on top of a testmethod
3. Build and run tests

Expected behavior

Mentioned item should get copied over to deployment directory

Actual behavior

No item is copied.

[AbhitejJohn]

Removed this from the UWP platform since deployment in UWP to another folder outside of the appx is a security concern and is not supported. Leaving this as a no-op in the .Net Core and filed #96 to track adding this support.