Add EXIF, IPTC, XMP metadata handling for JPEG, PNG, WEBP, GIF, HEIC, JXL, AVIF

[ausi]

I played around a little and parsing metadata works fine (PNG, WEBP and JPEG for now).

But writing metadata will probably be more dificult, as there are no counterparts to iptcparse() and exif_read_data() in PHP. So we will need to write the binary format ourselfs.

So I think to make this possible we need to define a list of fields we want to support (see #80 (comment) ) because supporting all EXIF, IPTC and XMP tags would be way too much work.

For XMP we could maybe find useful information in the https://github.com/wikimedia/xmp-reader library.

[ausi]

I investigated an Adobe stock image and the following tags seem to be relevant:

	IPTC	XMP	EXIF
Copyright-Hinweis	2#116	dc:rights	Copyright (8298)
Ersteller	2#080	dc:creator	Artist (013b)
Foto ID	2#115	photoshop:Source
Anbieter	2#110	photoshop:Credit, pur:creditLine

iStock (by Getty Images)

	IPTC	XMP	EXIF
Ersteller	2#080	dc:creator	Artist (013b) Copyright (8298)
Foto ID	2#005	dc:title, GettyImagesGIFT:AssetID
Anbieter	2#110	photoshop:Credit
Lizenz-URL		plus:Licensor

Fotolia

	IPTC	XMP	EXIF
Foto ID	2#115
Copyright	2#110, 2#116

[ausi]

Reading from PNG, WEBP and JPEG and writing to JPEG already works now 🎉 (Independent of Imagick/GD)

[ausi]

Reading and writing XMP, IPTC-IIM, EXIF from/to JPEG, PNG, WEBP works now 🚀

[m-vo]

This looks very nice and very powerful! ❤️
Nitpicks in the comments but the general concept is 👍