PERF: Improve FunctorImageFilter performances

Summary

Improve slightly the performances of otb::ImageFunctorFilter.

Rationale

otb::ImageFunctorFilter with a lambda is slightly less performant than itk::UnaryFunctorImageFilter with a dynamic functor.

Implementation Details

itk::UnaryFunctorImageFilter only updates the progress reporter once per line.

This MR mimics ITK behaviour.

Results

The performance improvement is small, less than 10% on simple filters like a scaling filter that multiplies pixel values. The gap seems to have been filled.

Copyright

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

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Check before merging:

• All discussions are resolved
• At least 2 votes from core developers, no vote.
• The feature branch is (reasonably) up-to-date with the base branch
• Dashboard is green
• Copyright owner has signed the ORFEO ToolBox Contributor License Agreement

On the subject, does anybody know why something similar (C++14) to

std::apply([](auto&& it){ it.NextLine();}, InputIterators); // ~ C++17

hasn't been done along side outIt.NextLine();?

Added to dashboard testing

merged

mentioned in commit b28c5338

added refactoring label

changed milestone to %7.0.0