Completion on first structure field should not fallback to top-level

```haxe
typedef Foo = {
?someField:String,
?secondField:Int,
}

class Main {
static function main() {
final foo:Foo = {
s|
secondField: 10,
}
}
}
```
4.2.5 (`secondField` can be detected and filtered from completion on vshaxe side, i think, fields after first comma are parsed and filtered already):
Upd: cannot reproduce this result anymore, my mistake, happens only if you trigger completion first and then write `s`

dev:

Start with the supplied Haxe snippet and reproduce completion after triggering completion first, then typing `s`; compare that behavior with the result after typing `s` before triggering completion. Done means completion on the first structure field remains scoped to the structure fields rather than falling back to top-level suggestions.

Written by the indexing model from the issue text.