Refactor macOS cursor code (#2463)

src/platform_impl/macos/appkit/image.rs

@@ -0,0 +1,37 @@
+use objc2::foundation::{NSData, NSObject, NSString};
+use objc2::rc::{Id, Shared};
+use objc2::{extern_class, extern_methods, msg_send_id, ClassType};
+
+extern_class!(
+    // TODO: Can this be mutable?
+    #[derive(Debug, PartialEq, Eq, Hash)]
+    pub(crate) struct NSImage;
+
+    unsafe impl ClassType for NSImage {
+        type Super = NSObject;
+    }
+);
+
+// Documented Thread-Unsafe, but:
+// > One thread can create an NSImage object, draw to the image buffer,
+// > and pass it off to the main thread for drawing. The underlying image
+// > cache is shared among all threads.
+// <https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/Multithreading/ThreadSafetySummary/ThreadSafetySummary.html#//apple_ref/doc/uid/10000057i-CH12-126728>
+//
+// So really only unsafe to mutate on several threads.
+unsafe impl Send for NSImage {}
+unsafe impl Sync for NSImage {}
+
+extern_methods!(
+    unsafe impl NSImage {
+        pub fn new_by_referencing_file(path: &NSString) -> Id<Self, Shared> {
+            let this = unsafe { msg_send_id![Self::class(), alloc] };
+            unsafe { msg_send_id![this, initByReferencingFile: path] }
+        }
+
+        pub fn new_with_data(data: &NSData) -> Id<Self, Shared> {
+            let this = unsafe { msg_send_id![Self::class(), alloc] };
+            unsafe { msg_send_id![this, initWithData: data] }
+        }
+    }
+);