Enable support for ISO/IEC 23008-12:2017 HEIF/HEIC image format

Packages describing “heif” as local USE flag

Package“heif” Flag Description
media-libs/imlib2Heif and Avif image loader support
media-libs/jasperEnable experimental support for HEIF/HEIC, unsupported by upstream

All packages providing a “heif” USE flag (17)