Improve subsequent iOS build times by caching iOS build configurations and build settings, fingerprint Xcode project and related files

[jmagman]

Cache discovered build configurations (for flavors), build settings, if you have a watch companion, architecture constraints of particular pods, etc by Fingerprintering all the files in Runner.xcodeproj/ and storing them somewhere in build/. This will improve flutter build ios/ run times.

Similar to how pod install is skipped:

flutter/packages/flutter_tools/lib/src/macos/cocoapod_utils.dart

Lines 24 to 26 in b9caef5

	// If the Xcode project, Podfile, or generated xcconfig have changed since
	// last run, pods should be updated.
	final Fingerprinter fingerprinter = Fingerprinter(