[File chooser widget] Moving through the directory structure by mouse arrow buttons
It’s possible to use "Alt + Arrow-Up/Down" but this doesn’t apply to the mouse buttons "Forward/Backward".
In Nautilus those buttons seem to be mapped to "Alt + Arrow-Left/Right", what isn’t implemented in the file chooser widget, so these buttons need to be mapped to "Alt + Arrow-Up/Down" there, for making them work.