Add more test coverage for tooling/RevEng

[ajcvickers]

No description provided.

[smitpatel]

@bricelam - Heads up. I am going to start working on modifying reveng tests as we discussed earlier.

[smitpatel]

Summary of a recent discussion about testing of tools interface
There are 3 splits of tests needed.

1. PMC/dotnet ef calling into mock ef.exe with correct parameters.
2. ef.exe calling into mock executor.
3. Executor calling into right entry points into (mock) design assembly.

Above would verify, from command to design assembly entry point pipeline is working correctly.
Inside design assembly there are tests based on the scenarios.

[bricelam]

We also intend to add some IModel -> C# tests. (started in bricelam:gen)