Add HDR-enabled HEIF option to video snapshot function and loadable image file format

VLC media player can play HDR videos, but it seems that video snapshot function can't save HDR still images.\

HEIF container format can store HEVC-encoded images including HDR-enabled Main10 profile.\

It will be useful to be add HEIF option to video snapshot function and add it to loadable image file format as well.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information