ecpg: move some functions into a new file ecpg/preproc/util.c.
mm_alloc and mm_strdup were in type.c, which seems a completely
random choice. No doubt the original author thought two small
functions didn't deserve their own file. But I'm about to add
some more memory-management stuff beside them, so let's put them
in a less surprising place. This seems like a better home for
mmerror, mmfatal, and the cat_str/make_str family, too.
Discussion: https://postgr.es/m/
2011420.
1713493114@sss.pgh.pa.us