[JetStream] Migrate the bringIntoViewIfChildrenAreFocused modifier from composed function to Modifier.Node

- The `bringIntoViewIfChildrenAreFocused` modifier uses `composed` function.
- The `composed` function causes the whole modifier chain to be re-composed every time.
- The `bringIntoViewIfChildrenAreFocused` modifier should switch its implementation to Modifer.Node for better performance.

Locate the bringIntoViewIfChildrenAreFocused definition in the JetStream sample and inspect nearby Modifier.Node implementations first. Migrate this modifier away from composed while preserving its behavior, then run the sample's available checks to confirm it still builds and the modifier works as before.

Written by the indexing model from the issue text.