`@children[<NUMBER>]` to index into the `@children` array

[hunger]

We want to make @children more useful.

While we got stuck with naming children, we all agreed that indexing into the "array" of @children makes sense.

I plan to implement this.

I want the compiler to support @children[x] where x is a NumberLiteral. This is the simplest possible use case and several @children[x] are allowed in a componant.

• The first child will be @children[0], to stay compatible with array indices in slint.

• If x @children[...] are used in a component, then

  • you must have one @children[y] for all y in [0; x[
  • you must provide exactly x children when using the component.