Issue Description:

As discussed on this thread:

https://forums.swift.org/t/swift-package-update-xcodeproj/21794

When actively developing a server side app in Xcode using SPM it can be a pain adding new package dependencies and then running

1. swift package update

2. swift package generate-xcodeproj

when the Xcode project contains scheme configuration information such as runtime args or environment variables as this information is immediately lost and has to be re-input.

A workaround suggestion on the thread is to create a workspace file separate from the Xcode project file, however I think a new alternate command of "update-xcodeproj" that just updates the dependency related information of the Xcode project file would be simpler and a good improvement to the developer experience in Xcode if made available.