Need to extend pypeit_parse_slits functionality to all Calibration types

[jhennawi]

Current pypeit_parse_slits prints out a summary of masked slits for Slits* objects and spec2d objects. We should be able to check every step of the calibration this way to help debug what went wrong. Best would be if any of the files in Calibrations could be read in with pypeit_parse_slits resulting in a diagnosis of which slits are masked.

[profxj]

This functionality exists but could be better documented and
improve the script name (e.g. pypeit_slit_report)

[kbwestfall]

Based on your response, @profxj , can this be closed?