With ARM Apple Silicon simulators (and Catalyst, though Flutter doesn't directly support it), distributing universal binaries is no longer possible since the arm64 iphonesimulator and arm64 iphoneos binaries can't be lipod together. Always produce xcframeworks, which is the preferred method of binary distribution.

flutter build ios-framework should default to producing xcframeworks instead of universal binaries.

xcframework was introduced in Xcode 11 which is also Flutter's minimum supported version.

Samples updated at flutter/samples#582.