Fix function unnamed argument types not being resolved correctly

[insertt]

This PR fixes issue with functions that have unnamed arguments not being parsed correctly and in result types of the parameters are incorrectly resolved.

Previously, function declarations such as:

module glfw;

def WindowRef = void*;
def MonitorRef = void*;

extern fn WindowRef createWindow(int, int, char*, MonitorRef, WindowRef) @extern("glfwCreateWindow");

were parsed and resolved into this form that had incorrect types:

but with this change, they're now correctly resolved and unnamed parameters have generic parameter names in format $arg{position} to not clash with other possible declarations:

[pherrymason]

Thank you!