Propagate access dependencies for ternary expressions in pure functions

[AlexFalter]

In this PR we introduce conditional heap-dependent expressions in pure functions. Namely, we extend the already existing model, which passed access dependencies unconditionally, and extend it by a condition. On field access or function usage, instead of encoding an expression as an unconditional access, we create a ternary expression unfolding predicates depending on the condition under which what predicates have to be unfolded. To validate our implementation we have created various test cases

[jesyspa]

I am still quite concerned about this case:

class Box(inner: Box?)
fun f(x: Box?, y: Box?): Box? = (x ?: y)?.inner?.inner

It seems to me like the current approach will not correctly unfold permissions, but maybe I'm missing something.

I'll test it out and get this merged if it's okay - no action needed on your part.