Add documentation about mode_shape to the Exodus reader.

Change-Id: Iedbb901685be021f976ef17ed28d6f8fb31cb148
Move VTK: Rename data_index to mode_shape in Exodus reader.

Change-Id: I30eb9c26e630c96102e60c91c7c64be1199769c2
Merge topic 'exodus-15127' into next

528499cb Move VTK: Rename data_index to mode_shape in Exodus reader.
c2fa5379 Add documentation about mode_shape to the Exodus reader.