Cleanup `AST::MacroInvocation` class

[CohenArthur]

The current implementation inherits from a lot of base classes, which is necessary, but does not always constructs all of them. Both of its constructors do not call into the same base class constructors for example. Similarly, this class has a lot of duplicate members with its base classes (locus, node_id) which we need to sort out

[badumbatish]

i think i can do this