Restructure cocoa crate

[komi1230]

In the future, directory structure should be like below:

src
├── appkit
│   ├── text.rs
│   ├── view.rs
│   └── etc...
├── swiftui
│   ├── text.rs
│   ├── view.rs
│   └── etc...
├── uikit
│   ├── text.rs
│   ├── view.rs
│   └── etc...
├── util
│   ├── base.rs
│   ├── foundation.rs
│   └── etc...
├── appkit.rs
├── swiftui.rs
├── uikit.rs
├── util.rs
├── lib.rs
├── macros.rs
└── quartzcore.rs

But current cocoa dir structure is like below:

src
├── appkit.rs
├── base.rs
├── foundation.rs
├── lib.rs
├── macros.rs
└── quartzcore.rs

These days I'm developing Winit to improve experience in IME. And I have found current cocoa crate has many points to be improved.
I want to contribute this crate with adding some class or protocol which is still not to be implemented, like NSTextInputClient or etc.
But there are too many class and protocol to be implemented. That's why I propose cocoa crate should be structured to be scalable to implement more features.
And also I propose to add swiftui/ and uikit/.
This structure can endure other issues about SwiftUI.

How do you think about this ?