Add Swift Package Manager Support to a Capacitor Plugin

Make a plugin installable in SPM-based Capacitor apps while keeping its podspec for CocoaPods apps.

When to Use

TRIGGER when:

• A plugin repo has ios/Plugin/*.swift + *.m/*.h with CAP_PLUGIN(...) and no root Package.swift.
• An app's npx cap sync ios prints <plugin id> does not have a Package.swift for a plugin the user maintains.
• A plugin works with CocoaPods but JS gets "X" plugin is not implemented on ios in SPM apps.
• Preparing a plugin for Capacitor 9 / CocoaPods Trunk read-only.

Do not use:

• App-side CocoaPods removal -> cocoapods-to-spm.
• Capacitor major bumps of a plugin -> capacitor-plugin-upgrades, capacitor-plugin-upgrade-v8-to-v9.
• Android-only plugin work, or non-Capacitor (pure Cordova, React Native) plugins.

Rules the CLI Enforces (non-obvious)