drive: add --drive-skip-dangling-shortcuts flag - fixes #5949

This flag enables dangling shortcuts to be skipped without an error.

backend/drive/drive.go

@@ -553,6 +553,14 @@ Google don't document so it may break in the future.
 Normally rclone dereferences shortcut files making them appear as if
 they are the original file (see [the shortcuts section](#shortcuts)).
 If this flag is set then rclone will ignore shortcut files completely.
+`,
+			Advanced: true,
+			Default:  false,
+		}, {
+			Name: "skip_dangling_shortcuts",
+			Help: `If set skip dangling shortcut files.
+
+If this is set then rclone will not show any dangling shortcuts in listings.
 `,
 			Advanced: true,
 			Default:  false,
@@ -616,6 +624,7 @@ type Options struct {
 	StopOnUploadLimit         bool                 `config:"stop_on_upload_limit"`
 	StopOnDownloadLimit       bool                 `config:"stop_on_download_limit"`
 	SkipShortcuts             bool                 `config:"skip_shortcuts"`
+	SkipDanglingShortcuts     bool                 `config:"skip_dangling_shortcuts"`
 	Enc                       encoder.MultiEncoder `config:"encoding"`
 }
 
@@ -918,6 +927,11 @@ OUTER:
 				if err != nil {
 					return false, fmt.Errorf("list: %w", err)
 				}
+				// leave the dangling shortcut out of the listings
+				// we've already logged about the dangling shortcut in resolveShortcut
+				if f.opt.SkipDanglingShortcuts && item.MimeType == shortcutMimeTypeDangling {
+					continue
+				}
 			}
 			// Check the case of items is correct since
 			// the `=` operator is case insensitive.