[shove70]

1. Fixed type Tree =string | map[string]string confuse v  #19811
2. Add tests.

type Tree = string| map[string]string

fn append(mut tree Tree) {
    print(tree["key"])
}

fn main() {
}

outputs:

a.v:4:15: error: type `Tree` does not support indexing
    2 | 
    3 | fn append(mut tree Tree) {
    4 |     print(tree["key"])
      |               ~~~~~~~
    5 | }
    6 |