GIN pending list clean up exposure to SQL

I've written a function which allows users to clean up the pending list.
It takes the index name and returns the number of pending list pages
deleted.

# select * from gin_clean_pending_list('foo_text_array_idx');
gin_clean_pending_list
------------------------
278
(1 row)

Time: 31994.880 ms

This is needed because there needs to be a way to offload this duty from
the user backends, and the only other way to intentionaly clean up the list
is by vacuum (and the rest of a vacuum can take days to run on a large
table). Autoanalyze will also do it, but it hard to arrange for those to
occur at need, and unless you drop default_statistics_target very low they
can also take a long time. And if you do lower the target, it screws up
your statistics, of course.

I've currently crammed it into pageinspect, simply because that is where I
found the existing code which I used as an exemplar for writing this code.

But where does this belong? Core? Its own separate extension?

Cheers,

Jeff