Add Test-DscResource Function

[michaeltlombardi]

As an engineer developing and maintaining DSC Resources, I want to be able to validate that a DSC Resource is defined properly per the implementation specification, checking for anti-patterns and best practices to improve the DevX for writing and maintaining DSC Resources and to reduce the number of defects I ship.

This functionality is wholly separate from calling Invoke-DscResource with the Test method; the goal is to assure the quality/validity of the implementation of the resource from DSC's perspective, not the end user's. That testing is more appropriately covered by unit, integration, and acceptance testing (which the command could arguably support, but is out of scope for this suggestion).