BUG #15632: Fix exodus performance issue with spatial files.

When files in an exodus file series were spatial partitions, reading timesteps from each one of them is not only wasteful but also slows down the reader considerably. In this fix, we update vtkPExodusIIReader to pass the timesteps information from the first reader to all the rest and avoid the other filters from re-reading the time information. Since the reader has to skip through files to read time information, it can have a serious performance impact. This fix addresses the issue with minimal refactoring of the reader.