[Feature]: Power Fx Test Steps namespace requirements for MEF Functions

[Grant-Archibald-MS]

Is your feature request related to a problem? Please describe.

The MEF extensibility model of the Test Engine allows additional test Power Fx functions to be loaded via ReflectionFunction. This could cause conflicts with out of the box functions or future updates to Power Fx functions.

Describe the solution you'd like

Enforce that all ReflectionFunction in a Test Engine model must:

• Use the DPath overload of reflection function overload
• Use a DPath not the Root namespace
• Include Assembly scans to enforce namespace has been applied

Sample implementation using DPath.Root.Append(new DName("Common") to add a function to Common namespace.

Describe alternatives you've considered

No response

Additional context?

No response