graphics/exiv2: upgrade to 0.28

Add DOCS and DOXYGEN options to allow building/installing
extra documentation.

Cherry-pick a few fixes from the upstream Git repo,
and add one FreeBSD-specific fix to libprocinfo interface
that caused crashes in the test rig, and add
sscanf/printf vs type fixes.

Fix a few things in exiv2 and Adobe XMP SDK found while
test-compiling exiv2 consumers.

All local fixes to .cpp filed with upstream repo as pull req.

While here, reformat/rearrange to please portlint and
portfmt/portclippy.

Assisted and
Reviewed by:		diizzy@
PR:                     272311
Differential Revision:  https://reviews.freebsd.org/D40828