add homescreen widget skill

[mariamhas]

This PR adds the flutter-home-screen-widget skill to the repository, providing a standardized workflow for implementing native widgets on iOS and Android. It simplifies the complex process of cross-platform data sharing and native UI rendering using the home_widget package, enabling developers to easily extend their Flutter apps to the home screen.

Pre-launch Checklist

• [ x] I read the Contributor Guide and followed the process outlined there for submitting PRs.
• [ x] I read the Tree Hygiene wiki page, which explains my responsibilities.
• [x ] I read the Flutter Style Guide recently, and have followed its advice.
• [x ] I signed the CLA.
• [ x] I listed at least one issue that this PR fixes in the description above.
• [x ] I updated/added relevant documentation (doc comments with ///).
• [x ] I added new tests to check the change I am making, or this PR is test-exempt.
• [ x] All existing and new tests are passing.

[jwren]

🎉 LGTM!

[johnpryan]

LGTM