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/button.rs

@@ -0,0 +1,14 @@
+use objc2::foundation::NSObject;
+use objc2::{extern_class, ClassType};
+
+use super::{NSControl, NSResponder, NSView};
+
+extern_class!(
+    #[derive(Debug, PartialEq, Eq, Hash)]
+    pub(crate) struct NSButton;
+
+    unsafe impl ClassType for NSButton {
+        #[inherits(NSView, NSResponder, NSObject)]
+        type Super = NSControl;
+    }
+);