saturationDetection: apply to overscan as well as image

The overscan may be saturated from charge bleeding in from
the image.
defects: activate useFallbackValueAtEdge for interpolation

Lack of use of this feature meant that NANs were not being
interpolated over.
Merge branch 'tickets/HSC-1030'
Use amp.getDiskBiasSec() instead of amp.getBiasSec() in saturationDetection()
Merge branch 'tickets/HSC-1037': Rotated chips will fail in saturationDetection
IsrTask: Add function to set valid Polygon

This is currently used only in the obs_subaru isr task.  It was put here
to make pushing to the LSST side easier.
Merge branch 'tickets/HSC-976'