[CMake] Refactor --xcode To Imply --skip-build

[CodaFi]

Erik shared a workflow for using the Ninja build tool with the generated CMake xcode project. Since --xcode's build powers have been busted for quite some time, this seems like a way to get the best of both worlds, even if it's a little bit manual.

Steps here:

• Expand Erik's documentation on integrating Ninja with Xcode into a proper tutorial #61907
• Make --xcode imply --skip-build --skip-early-swift-driver #61906
• Make --xcode emit a warning about the generated projects that links out to integration with Ninja tutorial #61910

Stretch goals:

• Contributor Experience: Automate the Xcode workspace generation process #70604
• Look into generating a Grand Unified Swift Package for this

Additional discussion on Swift Evolution: https://forums.swift.org/t/remove-deprecate-xcode-option-from-build-script/59706