pageinspect: Improve page_header() for pages of 32kB

pageinspect: Improve page_header() for pages of 32kB

ld_upper, ld_lower, pd_special and the page size have been using
smallint as return type, which could cause those fields to return
negative values in certain cases for builds configures with a page size
of 32kB.

Bump pageinspect to 1.10.  page_header() is able to handle the correct
return type of those fields at runtime when using an older version of
the extension, with some tests are added to cover that.

Author: Quan Zongliang
Reviewed-by: Michael Paquier, Bharath Rupireddy
Discussion: https://postgr.es/m/8b8ec36e-61fe-14f9-005d-07bc85aa4eed@yeah.net