File.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 [gio.file_monitor.FileMonitor] to track those properties, so this function needs to be called instead. Creating lots of [gio.file_monitor.FileMonitor]'s would take lots of resources.

Since this function is synchronous, it is advised to call it only on local files. See [gtksource.file.File.isLocal].