parser, checker: fix var scope in lambda(fix #19860)

[shove70]

1. Fixed Uncaptured variable #19860
2. Add tests.

fn f(g fn (int) string) {
        println('function returned: ${g(42)}')
}
fn main() {
        s := 'hello world'
        f(|i| s)
}

outputs:

a.v:5:9: warning: unused variable: `s`
    3 | }
    4 | fn main() {
    5 |         s := 'hello world'
      |         ^
    6 |         f(|i| s)
    7 | }
a.v:6:15: error: undefined variable `s`
    4 | fn main() {
    5 |         s := 'hello world'
    6 |         f(|i| s)
      |               ^
    7 | }
    8 |
a.v:6:11: error: `s` used as value
    4 | fn main() {
    5 |         s := 'hello world'
    6 |         f(|i| s)
      |           ^
    7 | }
    8 |