include: util: add array for-each macros

AFAIK, we do not have array for-each loops. Seemed like an
obvious gap to fill, so introduce two variants:

* ARRAY_FOR_EACH(array, idx_var)
* ARRAY_FOR_EACH_PTR(array, ptr_var)

Signed-off-by: Christopher Friedt <cfriedt@meta.com>