Support iOS Icon Composer app icons in Very Good Core template & docs

[AristideVB]

Description

When generating a Flutter app with Very Good CLI using the Very Good Core template, the iOS app icon flow still relies on the legacy asset catalog approach. I’d like the template and docs to adopt Apple’s new Icon Composer–based workflow so that new projects are ready for modern iOS app icons (including glass icons) out of the box.

Relevant docs:

• Very Good CLI – Updating App Icons: https://cli.vgv.dev/docs/templates/core#updating-app-icons-
• Apple – Creating your app icon using Icon Composer: https://developer.apple.com/documentation/xcode/creating-your-app-icon-using-icon-composer#Add-your-Icon-Composer-file-to-an-Xcode-project

Requirements

• Update the Very Good Core iOS template to define the app icon via an Icon Composer file (for example AppIcon.icon) rather than only a classic image set in Assets.xcassets.
• Ensure the generated project works with current Xcode defaults and supports glass app icons where available.
• Update the “Updating App Icons → iOS” docs to describe the Icon Composer workflow and reference the Apple docs above.
• Keep the change backwards compatible for existing users as much as reasonably possible (no breaking changes to the CLI interface).

Additional Context

No response

[ricardodalarme]

Thanks for opening this issue @AristideVB, I'll check that