Add "LP_DEAD item?" column to GiST pageinspect functions
This brings gist_page_items() and gist_page_items_bytea() in line with
nbtree's bt_page_items() function.
Minor follow-up to commit
756ab291, which added the GiST functions.
Author: Andrey Borodin <x4mmm@yandex-team.ru>
Discussion: https://postgr.es/m/
E0794687-7315-4C29-A9C7-
EC54D448596D@yandex-team.ru