macos: View-based FileOutlineView (#7760)

Signed-off-by: Dzmitry Neviadomski <nevack.d@gmail.com>

macosx/FileCheckCellView.h

@@ -0,0 +1,13 @@
+// This file Copyright © Transmission authors and contributors.
+// It may be used under the MIT (SPDX: MIT) license.
+// License text can be found in the licenses/ folder.
+
+#import <AppKit/AppKit.h>
+
+@class FileListNode;
+
+@interface FileCheckCellView : NSTableCellView
+
+@property(nonatomic, weak) FileListNode* node;
+
+@end