Fix handling of SAR Metadata (with empty projection)

Summary

Make sure SAR metadata are not improperly discarded.

Rationale

When a projection is set with SetProjectionRef(), it sets MDGeom::ProjectionWKT which in turn prevents SAR metadata to be written into the final file in GDALImageIO::InternalReadImageInformation().

The problem arises when the projection is an empty string. This quickly happens on innocent lines like:

outputPtr->SetProjectionRef(m_SarImagePtr->GetProjectionRef());

(that we could find in DiapOTB otbSARDEMPolygonsAnalysisImageFilter.hxx or related filters like the improved fork in https://gitlab.orfeo-toolbox.org/s1-tiling/normlim_sigma0 or Gamm0 RTC implementation)

Implementation Details

1. Have SetProjectionRef clear MDGeom::ProjectionWKT metadata on empty string
2. Test not only Has(MDGeom::ProjectionWKT) in GDALImageIO::InternalReadImageInformation() but also whether the projections are empty
3. And warn SAR metadata will be discarded if they are detected while there is a projection that supersedes their serialization

Bonus

• Some warnings are handled:

  • Add OTB_FALLTHROUGH as we can't use C++17 [[fallthrough]] yet.
  • Make otbUnusedMacro depend on the one and only symbol that really decides whether an assertion is expanded or not => NDEBUG and not OTB_DEBUG

• Remove an undefined behaviour on extracting some SAR std::array metadata (MRE: https://gcc.godbolt.org/z/9s6Gsrz1x)

• Error messages on missing metadata are improved

  • for instance: instead of an exception that reports an error on map::at, we will correctly signal that GCP are not present in the metadata
  • more context is also provided for many other metadata; and code is simplified thanks to helper functions

• Some other minor code improvements and optimisations

• Possibly related to #2266. Further tests are required. EDIT -> no changes

Copyright

The copyright owner is CNES and has signed the ORFEO ToolBox Contributor License Agreement.

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