This provides variable capture in standard situations:
- nested functions
- lambdas
There are some deficiencies:
- we do not yet handle objects capturing variables.
- we do not handle variables captured via the `nonlocal` keyword.
  This should be solved at the AST level, though, and then it
  should "just work".

There is still inconsistencies the case of where
a `SynthesizedCaptureNode` has a comprehensions
as its enclosing callable. In this case,
`TFunction(cn.getEnclosingCallable())` is not
defined and so getEnclosingCallable does not exist
for the `CaptureNode`.

an extra node is now in play.

TODO:
The member predicate `LibraryLambdaMethod::getACall` is
currently too permissive.
Ideally, we would have `libraryCallHasLambdaArg`
as in Ruby. But even a more precise
`libraryCall` predicate might be fine.

On the small test project, this reduces the number
of instances from 285 to 22.

as in Ruby