Add support for the QOI image format

This MR adds read-only QOI (https://qoiformat.org/) image format support for KImageFormats.

This format has received it's MIME type inclusion in shared-mime-info 4 months ago: ff51a0a9e3

The code is based on the reference QOI implementation at https://github.com/phoboslab/qoi/blob/master/qoi.h

Official test images: https://qoiformat.org/qoi_test_images.zip

![pngvsqoi](/uploads/e386aa5057641057106e21940c770d97/pngvsqoi.png)

Also: This is my first MR to KDE ;)
(cherry picked from commit b209e54b6f)

src/imageformats/qoi.json

@@ -0,0 +1,4 @@
+{
+    "Keys": [ "qoi" ],
+    "MimeTypes": [ "image/qoi" ]
+}