PicZip image conversion dependencies

@su-engineering/heic 0.2.0 (MIT): https://github.com/su-engineering/heic
License: /licenses/heic.txt

libheif-js 1.23.5 (LGPL-3.0): https://github.com/catdad-experiments/libheif-js/tree/v1.23.5
Unmodified npm distribution, loaded as a separate browser worker dependency.
License: /licenses/libheif-js.txt
Library source and build instructions: https://github.com/catdad-experiments/libheif-js
Underlying libheif source: https://github.com/strukturag/libheif
To replace the library, install your compatible libheif-js build and rebuild PicZip.

pdf-lib 1.17.1 (MIT): https://github.com/Hopding/pdf-lib
License: /licenses/pdf-lib.txt