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ARROW-10776: [C++] Allow STL iteration over concrete primitive arrays

This is a useful primitive when maximum performance isn't required, for example when testing.

Closes #8806 from pitrou/ARROW-10776-array-iterator

Lead-authored-by: Antoine Pitrou <antoine@python.org>
Co-authored-by: Benjamin Kietzman <bengilgit@gmail.com>
Signed-off-by: Antoine Pitrou <antoine@python.org>