[FEA]: Implement iterator concepts and update <iterator> to C++20

[jrhemstad]

<ranges> require a lot of machinery in place to work. This includes the various concepts, e.g. std::contiguous_iterator but also iterator traits.

As a first step of the <ranges> implementation we should implement those and update all the machinery in <iterators>

Tasks

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1. [FEA] Implement iter_move #206
   feature request libcu++ +2
   
2. [FEA]: Implement iterator concepts #247
   +0
   
3. Implement iter_swap CPO #337
   feature request libcu++ +2
   
4. Implement permutable concept #366
   +0
   
5. Implement identity helper #382
   +0
   
6. Implement projected helper #384
   +0
   
7. Implement indirectly_comparable concept #444
   +0
   
8. Implement ranges comparison objects #463
   +0
   
9. Implement sortable concept #470
   +0
   
10. Implement mergeable concept #483
    +0
    
11. Implement move_sentinel #495
    +0
    
12. Implement unreachable_sentinel #505
    +0
    
13. Implement __bounded_iter
14. Implement ranges::advance #545
    +0
    
15. Implement ranges::next #610
    +0
    
16. Implement ranges::prev
17. Implement ranges::distance
18. Modernize move_iterator
19. Cleanup <iterator>
20. Modernize reverse_iterator
21. Modernize wrap_iter

[miscco]

Done with #627