Refactor macOS to use new objc2 features (#2465)

* Remove UnownedWindow::inner_rect

* Refactor custom view to use much less `unsafe`

The compiler fence is safe to get rid of now since `interpretKeyEvents` takes `&mut self`

* Refactor Window to use much less unsafe

* Refactor NSApplication usage to have much less unsafe

* Remove cocoa dependency

* Enable `deny(unsafe_op_in_unsafe_fn)` on macOS

Also re-enable clippy `let_unit_value` lint

* Remove #[macro_use] on macOS

* Refactor window delegate to use much less unsafe

src/platform_impl/macos/appkit/pasteboard.rs

@@ -0,0 +1,26 @@
+use objc2::foundation::{NSObject, NSString};
+use objc2::rc::{Id, Shared};
+use objc2::{extern_class, extern_methods, msg_send_id, ClassType};
+
+extern_class!(
+    #[derive(Debug, PartialEq, Eq, Hash)]
+    pub(crate) struct NSPasteboard;
+
+    unsafe impl ClassType for NSPasteboard {
+        type Super = NSObject;
+    }
+);
+
+extern_methods!(
+    unsafe impl NSPasteboard {
+        pub fn propertyListForType(&self, type_: &NSPasteboardType) -> Id<NSObject, Shared> {
+            unsafe { msg_send_id![self, propertyListForType: type_] }
+        }
+    }
+);
+
+pub type NSPasteboardType = NSString;
+
+extern "C" {
+    pub static NSFilenamesPboardType: &'static NSPasteboardType;
+}