Use more palloc_object() and palloc_array() in contrib/

Use more palloc_object() and palloc_array() in contrib/

The idea is to encourage more the use of these new routines across the
tree, as these offer stronger type safety guarantees than palloc().  In
an ideal world, palloc() would then act as an internal routine of these
flavors, whose footprint in the tree is minimal.

The patch sent by the author is very large, and this chunk of changes
represents something like 10% of the overall patch submitted.

The code compiled is the same before and after this commit, using
objdump to do some validation with a difference taken in-between.  There
are some diffs, which are caused by changes in line numbers because some
of the new allocation formulas are shorter, for the following files:
trgm_regexp.c, xpath.c and pg_walinspect.c.

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