Rewrite cocoa crate to mirror Swift APIs instead of ObjC APIs

[mehcode]

Refs #200

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Thoughts on this? These crates are frustrating to use in Rust. Adapting the Swift APIs would lead to a significantly better UX in the API.

We could offer the Objective C API in addition to the Swift API for some backwards compatibility though I'm unsure if we could keep it 100% as the types are just id aliases now.

[jdm]

Can you give some examples of before and after? Which APIs are you referring to?

[mehcode]

By mirror Swift APIs I don't mean use the names and types that Swift does. I more meant use the approach that Swift took in wrapping Objective C and take liberty with naming and types to better match our host language, Rust.

Naming

As an example.. instead of NSWindowStyleMask::NSClosableWindowMask, we could have WindowStyleMask::CLOSABLE; instead of, window.makeKeyAndOrderFront_(nil) we could have window.make_key_and_order_front(None).

Safety

Nearly every line of cocoa code I write needs an unsafe { .. } block when its mostly "safe" in theory. We should be able to enforce safety.

I see there was some interest in #200.

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It looks like there have been a couple of attempts elsewhere to make things nicer, like in objrs.

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I don't really have a definitive plan. More just musing and would love to contribute to an effort to have a better overall native iOS/macOS dev experience in Rust.

[lqf96]

Just a random thought: we should leverage the toll-free bridging between Objective-C, Swift and CoreFoundation types in some way to minimize the work we need to do. This will also make interaction with Swift code easier.