cgen: fix ref and deref when interface as a function parameter(fix #19947)

[shove70]

1. Fixed Builder error : cannot convert 'struct main__Hittable' to 'struct main__Hittable *' #19947
2. Add tests.

interface Foo {}

fn main() {
	foo := Foo(1)
	thing(foo)
}

fn thing(src_objects Foo) {
	other_thing(src_objects, src_objects)
}

fn other_thing(a &Foo, b &Foo) {
	dump(a)
	dump(b)
}

outputs:

[a.v:14] a: &Foo(1)
[a.v:15] b: &Foo(1)