Stub API

[belka-ew]

Stub API would be a subset of the available Mocking API, but without the support for the expectations.

Differences:

• The builder doesn't need .verify and .expect() (but .stub())
• There is actually no need to make it a member function of the Mocker since there is no need to track created stubs; so stub!Object() can be a freestanding function
• Stubbed class requires less generated code, since we can skip expectation checking
• Repositories, overloads and calls can probably use the same data structures

[belka-ew]

A draft ist written.

It is Mocker.stub() so that the stub can use comparators set for the mocker.

Open questions:

• .repeat-functions aren't needed. It should be possible to use different Calls in stubs and mocks. Or .repeat can be a noop which is less nice.
• What happens if the given arguments don't match the set ones?
  • If there is a stub call configured without the arguments at all, it can be used as fallback-
  • if the Call queue is empty, return .init.