vtkAMReXGridReader: fix time reading.
Fixes a couple of issues:
- vtkAMReXGridReader was not announcing time values it read from the header; fixed that.
- vtkAMReXGridReader was not correctly detecting filename had changed. This was causing the reader to not read header information for additional files when reading a series; fixed that.
Addresses paraview/paraview#20222 (closed).
Backport: paraview/release