TF-3416 Handle open EML attachment in EML previewer

core/lib/data/model/preview_attachment.dart

@@ -0,0 +1,24 @@
+
+import 'package:equatable/equatable.dart';
+
+class PreviewAttachment with EquatableMixin {
+  final String iconBase64Data;
+  final String name;
+  final String size;
+  final String? link;
+
+  PreviewAttachment({
+    required this.iconBase64Data,
+    required this.name,
+    required this.size,
+    this.link,
+  });
+
+  @override
+  List<Object?> get props => [
+    iconBase64Data,
+    name,
+    size,
+    link,
+  ];
+}