Homesceen-Widgets support for iOS and Android

### What is the problem or limitation you are having?

Create native Homesceen-Widgets on Mobile platform

### Describe the solution you'd like

Maybe add a "widget.content"

### Describe alternatives you've considered

_

### Additional context

_No response_

Start by reviewing Toga's existing mobile architecture and platform entry points for iOS and Android. Clarify the proposed widget.content API and define what native home-screen widget support must provide on both platforms before implementation. Done should mean a documented, agreed design and working native widgets on iOS and Android.

Written by the indexing model from the issue text.