Support SwiftPM warning control build settings

Tuist can now load packages that use SwiftPM’s newer warning-control APIs, such as the ones used by swift-dependencies 1.13.0. The PackageInfo decoder handles treatAllWarnings, treatWarning, and enableWarning target build settings, and maps them to the same Xcode flags that SwiftPM uses. Previously, these unknown settings caused package decoding to fail before generation could begin.