Implement `View.positionWithAnchor` when intersection types are available

```kotlin
fun T.positionWithAnchor(position: Point, anchor: Anchor): T {
pos = position + size * Vector2(anchor.sx, anchor.sy)
this.anchor(anchor)
return this
}
```

alternatively:

```kotlin
fun T.positionWithAnchor(position: Point, anchor: Anchor): T {
pos = position + size * Vector2(anchor.sx, anchor.sy)
this.anchor(anchor)
return this
}
```

Start by locating the View, Anchorable, RectBase, Point, Vector2, and Anchor definitions and checking how existing positioning and anchor helpers are implemented. Determine whether the requested generic extension is supported by the available Kotlin intersection types, then verify that the chosen signature positions and returns the view as shown.

Written by the indexing model from the issue text.