Support Crossbow iOS Plugins

[enfipy]

Objective

It should be possible to create and use custom Crossbow iOS Plugins.

Useful links:

• https://github.com/godotengine/godot/tree/master/platform/ios
• https://docs.godotengine.org/en/stable/tutorials/platform/ios/ios_plugin.html
• https://docs.godotengine.org/en/stable/tutorials/platform/ios/plugins_for_ios.html