Use objc2 and its framework crates

`objc2` is a replacement for `objc`/`objc_id` that contains a bunch of safety improvements, including `msg_send_id!` which automatically upholds memory management rules (`Id::from_ptr`/`Id::from_retained_ptr` is no longer necessary).

Additionally, we use the framework crates `objc2-foundation` and `objc2-app-kit`, which provide for example the `NSPasteboard` type, which has the methods that arboard needs already defined, and with the correct types, ensuring that passing e.g. `Id<NSArray>` and thus accidentally giving away ownership over the array won't happen again.

These crates are automatically generated, ensuring that if you need some obscure API in the future, it's very likely to be there already.

Cargo.toml

@@ -33,9 +33,10 @@ clipboard-win = "5.3.1"
 log = "0.4"
 
 [target.'cfg(target_os = "macos")'.dependencies]
-objc = "0.2"
-objc_id = "0.1"
-objc-foundation = "0.1"
+# Use `relax-void-encoding`, as that allows us to pass `c_void` instead of implementing `Encode` correctly for `&CGImageRef`
+objc2 = { version = "0.5.1", features = ["relax-void-encoding"] }
+objc2-foundation = { version = "0.2.0", features = ["NSArray", "NSString", "NSEnumerator", "NSGeometry"] }
+objc2-app-kit = { version = "0.2.0", features = ["NSPasteboard", "NSPasteboardItem", "NSImage"] }
 core-graphics = { version = "0.23", optional = true }
 image = { version = "0.25", optional = true, default-features = false, features = ["tiff"] }