parser: fix shared generic struct as fn parameters(fix #19804)

[shove70]

1. Fixed Generic struct can't be used as shared method parameter #19804
2. Add tests.

struct Test[T] {
	value T
}

fn do_something(shared stuff Test[int]) {
	rlock stuff {
		println(stuff.value)
	}
}

shared test := Test[int]{}

do_something(shared test)

outputs:

0