file provider

Put App Documents in the System File Browsercodenameone.com

Codename One adds a read‑only DocumentProvider API that lets apps publish a virtual file tree to iOS Files and Android’s storage picker. The tree is defined with `DocumentNode` objects, can include remote‑only entries, and is shared via an App Group container. The iOS extension runs in a separate process, so the model is serialized and read independently; Android uses the same model inside the ap…