C++ named requirements: LegacyContiguousIterator (since C++17)

A LegacyContiguousIterator is a LegacyIterator whose logically adjacent elements are also physically adjacent in memory.

# Notes

Fancy pointer to object types are also required to satisfy LegacyContiguousIterator.

LegacyContiguousIterator is replaced with the contiguous_iterator concept: iterator types in the standard library that are required to satisfy LegacyContiguousIterator in C++17 are required to model contiguous_iterator in C++20.

# See also