Reinstate the ve-ui-toolbar-saveButton class

The class provided a minimal coupling to the firsteditve guided tour,
which used it to attach a guider to the "Save page" button.

The class was removed in I30dc7020121f0dd6907b61ef674a7cb14eb00652.

Bug: 69784
Change-Id: I81fdc4f2fa41c86a6481cf478c154b5d6c99d41d