Issue #8214: Add Quite-OK Image format support

This attempts to resolve issue #8214 (closed) by adding a plug-in to load and export Quite-OK Image files. The Quite-OK Image format is a fairly simple image format - It supports 8 bit RGB/RGBA files only. It claims comparable sizes to PNG with much reduced compression/decompression time.

The qoi.h library is used to read and write the image data - the plug-in just passes the pixel data to/from a layer's GEGL buffer.

Sample images (PNGs included for reference): https://qoiformat.org/qoi_test_images.zip

Note: I created and tested this by including qoi.h directly in GIMP. @Wormnest noted it would be better to retrieve that from a package repository and linked https://packages.debian.org/bookworm/source/qoi. I'm not sure how to connect to that in meson.build and Makefile - any pointers would be appreciated!