Add support for protected members

[kzu]

In v4:

mock.Protected().Setup("SendAsync", ...)

We should offer more compile-time safety in v5 for protected members, possibly with completion providers + analyzers

[stakx]

Just for completeness' sake, @kzu have you seen .Protected().As<T>() that we added in v4 a while ago? Quick demo in this post.

Defining a parallel interface just for tests of course isn't very nice if you have to manually do it & keep in sync with the protected members, but I imagine you could easily automate that using code fixes (like you have done for typed delegates needed for by-ref parameters).

[kzu]

Heya @stakx, I'm resuming work on v5 :). Perhaps it should leverage source generators to automatically create that T for you? 🤔

[stakx]

Oh, that would be neat. The big issue with Moq 4's .Protected().As<TProtectedMembers>() is just that, one needs to write an extra type just for testing. Would be great if that could be automated away.