ArrayUtils - reorganize and more tests

Two issues
1) Most functions in array_utils.h are declared at the top of the file, but some are declared somewhere in the middle. Move all function declarations to the top for consistency.
2) Many of the functions declared in the middle of the file don't have tests (I missed them). Add tests to TestArrayUtils.cpp

Start by comparing the declarations in array_utils.h with the existing cases in TestArrayUtils.cpp. Move the declarations to the file’s top and add coverage for the currently untested functions, then verify that the ArrayUtils tests pass.

Written by the indexing model from the issue text.