Jason Crain authored Jan 03, 2020 and Albert Astals Cid committed Aug 21, 2020

PopplerDocument's creation-date and mod-date properties are 32-bit unix
times, a.k.a. GTime, and will overflow in 2038. Deprecate these
properties and replace with creation-datetime and mod-datetime, which
are GDateTime instead, and add accessor functions.

Fixes #765