[Refactor] Extract #custom_build_settings from TargetInstaller#add_target

This allows to extend the custom build settings in the concrete target-class specific subclasses.
Ensure that the Aggregate Target doesn't link vendored dependencies

As either the user project or the frameworks are responsible for that aspect and this can cause issues with duplicate symbols.
[Spec][Integration] Rebuild to overwrite Aggregate Target's linker build settings
[Example] Delete de-integrated "Embed Pods Frameworks" build phase

This was done automatically by `rake examples:build` after deeb4fde44807cfde987f960bd5ce2b0f2ad08e2.