checkFileOnDisk

Checks synchronously the file on disk, to know whether the file is externally modified, or has been deleted, and whether the file is read-only.

#GtkSourceFile doesn't create a class@Gio.FileMonitor to track those properties, so this function needs to be called instead. Creating lots of class@Gio.FileMonitor's would take lots of resources.

Since this function is synchronous, it is advised to call it only on local files. See method@File.is_local.