New port: graphics/libheif

libheif is an ISO/IEC 23008-12:2017 HEIF file format decoder and encoder.

HEIF is a new image file format employing HEVC (h.265) image coding for the
best compression ratios currently possible.

libheif makes use of libde265 for the actual image decoding and x265 for
encoding. Alternative codecs for, e.g., AVC and JPEG can be provided as
plugins.

WWW: https://github.com/strukturag/libheif

PR: 230767
Submitted by: Sebastian Steinmetz <freebsd-2018@sebastiansteinmetz.ch>