eframe: Use objc2 and its framework crates (#4395)

These are a replacement to the `objc` and `cocoa` crates.

This PR prevents:
- An extra copy when creating `NSData`
- A memory leak when creating `NSImage`
- A memory leak when creating `NSString`

And is generally a readability improvement.

Note that we define `NSApp` manually for now, the implementation in
`objc2-app-kit` is currently suboptimal and wouldn't allow you to check
whether the NSApplication has been created or not.

Related: https://github.com/emilk/egui/issues/4219, this should nicely
coincide with the Winit `0.30` release.

---------

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

crates/eframe/Cargo.toml

@@ -178,8 +178,19 @@ wgpu = { workspace = true, optional = true, features = [
 
 # mac:
 [target.'cfg(any(target_os = "macos"))'.dependencies]
-cocoa = "0.25.0"
-objc = "0.2.7"
+objc2 = "0.5.1"
+objc2-foundation = { version = "0.2.0", features = [
+  "block2",
+  "NSData",
+  "NSString",
+] }
+objc2-app-kit = { version = "0.2.0", features = [
+  "NSApplication",
+  "NSImage",
+  "NSMenu",
+  "NSMenuItem",
+  "NSResponder",
+] }
 
 # windows:
 [target.'cfg(any(target_os = "windows"))'.dependencies]