Add image copy functionality.

Currently only supports Windows.
Close #260

lib/utils/clipboard_image.dart

@@ -0,0 +1,22 @@
+import 'dart:io';
+import 'dart:ui';
+
+import 'package:flutter/services.dart';
+
+Future<void> writeImageToClipboard(Uint8List imageBytes) async {
+  const channel = MethodChannel("venera/clipboard");
+  if (Platform.isWindows) {
+    var image = await instantiateImageCodec(imageBytes);
+    var frame = await image.getNextFrame();
+    var data = await frame.image.toByteData(format: ImageByteFormat.rawRgba);
+    await channel.invokeMethod("writeImageToClipboard", {
+      "width": frame.image.width,
+      "height": frame.image.height,
+      "data": Uint8List.view(data!.buffer)
+    });
+    image.dispose();
+  } else {
+    // TODO: Implement for other platforms
+    throw UnsupportedError("Clipboard image is not supported on this platform");
+  }
+}