parser, checker, cgen: implement generics anon fn (fix #15120)

[yuyi98]

This PR implement generics anon fn (fix #15120, fix #13253).

• Implement generics anon fn.
• Add test.

fn setter<T>(mut m map[T]int) fn (T, int) {
	return fn [mut m] <T>(x T, k int) {
		m[x] = k
	}
}

fn main() {
	mut m := {
		f32(0.1): 1
	}

	f := setter(mut m)
	f(0.2, 2)

	println(m)
	assert m == {
		f32(0.1): 1
		0.2:      2
	}
}

PS D:\Test\v\tt1> v run .
{0.1: 1, 0.2: 2}

fn closure<T>(input T) fn () T {
	return fn [input] <T>() T {
		return input
	}
}

fn main() {
	f := closure(123)
	println(f())
}

PS D:\Test\v\tt1> v run .
123