Add unit tests for method dispatch

[cyrille-artho]

We currently do not exhaustively test all possible configurations of method calls. It would be advantageous to have an overview of which tests are already there and which cases are covered:

1. Method call within the same class or to a superclass or inner class. (Three options)
2. Method call from/to instance/static method. (Four options)
3. Access modifiers. (Four options for caller and callee: 4^2).

Theoretically, 3 * 4 * 4^2 = 192 options are possible, but some are not allowed (a public superclass method must remain public).
A first step here is to model which combinations are possible and then write a table to see which cases are already tested. We want to test key cases of the remaining combinations, achieving at least pairwise coverage.

[cyrille-artho]

As a first step, let's look at what options are possible (including perhaps anonymous inner classes) and what the combinatorial complexity is. We can use PICT to model this: https://github.com/microsoft/pict