Xcode 15 beta compatibility

[ksuther]

Trying to update the generated Info.plist directly in the built product no longer works reliably with Xcode 15. Instead we now read the input Info.plist, write an updated Info.plist to a temporary location, then use the generated Info.plist as the Info.plist file in the target settings.

Note that this approach won't work if GENERATE_INFOPLIST_FILE is YES (which we don't use in our projects).

Also updates to Swift 5, builds a universal binary, and other cleanup.