Delegate Gradle and Xcode projects to user
At this moment, AUI_BUILD_FOR generates Gradle and Xcode projects for the consumer, as part of Android and iOS support, respectively. This prevents the consumer from modifying Kotlin/Swift code, as well as further configuration and integration with Android Studio/Xcode. This PR removes AUI_BUILD_FOR, in favor of better integration with Gradle and xcbuild.
Part of #368.
tldr I'm trying to ~~steal~~ mimic project structure of a Flutter application (#368) for Android and iOS, also I expect the same thing for Flatpak. I have a template project boilerplate for both that I'll probably push to example_app repo.
Also there are bridges from gradle/xcode to aui.boot that allow aui_app-enabled projects to advertise their kotlin/swift code. This is essentially similar to Flutter Plugin packages. (if anyone uses AUI though vcpkg or conan2 I don't expect that to break, although I want to :p)