Analyzer - theory data row inside theory data

[snailtempo]

Addresses issue #3113 - Add analyzer to flag using ITheoryDataRow inside of TheoryData

Includes:

• Analyzer to detect TheoryData<ITheoryDataRow> and stronger types
• Added code fix to suggest IEnumerable<ITheoryDataRow>
• Analyzer/Codefix tests

Note: This is my first time contributing to this project and also my first time writing a Roslyn analyzer, so I wasn’t completely sure about some of the design decisions. Feedback is very welcome!

For instance, I was not sure if a code fix should be provided in such a scenario:

TheoryData<ITheoryDataRow> GetData() { return null; } // Currently: Codefix enabled, but could lead to invalid code (depending on method implementation)

[snailtempo]

@dotnet-policy-service agree

[bradwilson]

Thanks! I'm consolidating the tests for better performance (the compilation process is extremely expensive, so I've been doing this to all the existing tests as time allows).