<discriminator> := _ <non-negative number> # when number < 10 := __ <non-negative number> _ # when number >= 10 extension := decimal-digit

Demangle MangledName into an AST, storing it into this->RootNode.

Handle C++'s ... quirky decl grammar by using the left & right distinction. Consider: int (*f(float))(char) {} f is a function that takes a float and