Add related project of libflif-Xcode and SDWebImageFLIFCoder, which is useful for Apple platforms' user.

[dreampiggy]

Add two libflif related projects.

• libflif-Xcode

This is a Xcode project configuration, to build libflif libary on All Apple Platforms, including iOS/macOS/tvOS/watchOS. As a dynamic framework, use static framework by user's configuration.

This can also include Carthage support. Which is a widelly used Cocoa dependency manager, to manage and build Cocoa/Cocoa Touch library on Apple platforms. It's popular in Cocoa/Cocoa Touch developers.

• SDWebImageFLIFCoder

This is a coder plugin library, for the favorite Cocoa/Cocoa Touch image loading framework SDWebImage. The framework is used widely cross the world. The coder plugin, can support FLIF images encoding && decoding for user who use this framework. This can also been used as a standalone library when you want High-Level API (Objective-C && Swift) to communicate with Cocoa/Cocoa Touch system framework.

[jonsneyers]

Thanks for the contribution!

Sorry for being so negligent/slow. The FLIF codec has been superseded by the JPEG XL codec, and I was too busy with jxl to keep an eye on the flif repo. Please consider moving any project that is using FLIF to use libjxl instead.