8257a055 added some IGNORE_DEPRECATIONS markers, but did not fix the underlying issue in ev-attachment, the use of GTime. This commit provides GDateTime variant alternatives for all the functions that still use GTime. This allows to straight-forward remove the deprecated functions after the GTK4 move.
The GDateTime mtime and ctime are added as fields in the EvAttachmentPrivate structure, but not presented as properties in EvAttachment. Those properties are completely used in Evince's codebase, and likely unnecessary.
In the same MR, adapt ev-poppler to make use of the new functions.
Together with !547 (merged) !529 (merged) !527 (merged) !536 (merged) I'm trying to get evince built with -Wdeprecated-declarations, so that we get a more modern code-base.