Use pg_malloc_object() and pg_alloc_array() variants in frontend code

Use pg_malloc_object() and pg_alloc_array() variants in frontend code

This commit updates the frontend tools (src/bin/, contrib/ and
src/test/) to use the memory allocation variants based on
pg_malloc_object() and pg_malloc_array() in various code paths.  This
does not cover all the allocations, but a good chunk of them.

Like all the changes of this kind (31d3847a37be, etc.), this should
encourage any future code to use this new style.

Author: Andreas Karlsson <andreas@proxel.se>
Discussion: https://postgr.es/m/cfb645da-6b3a-4f22-9bcc-5bc46b0e9c61@proxel.se