Use palloc_object() and palloc_array(), the last change

Use palloc_object() and palloc_array(), the last change

This is the last batch of changes that have been suggested by the
author, this part covering the non-trivial changes.  Some of the changes
suggested have been discarded as they seem to lead to more instructions
generated, leaving the parts that can be qualified as in-place
replacements.

Similar work has been done in 1b105f9472bd, 0c3c5c3b06a3 and
31d3847a37be.

Author: David Geier <geidav.pg@gmail.com>
Discussion: https://postgr.es/m/ad0748d4-3080-436e-b0bc-ac8f86a3466a@gmail.com