We have a new, improved string type coming up in AK (OOM aware, no null
state), and while it's going to use UTF-8, the name UTF8String is a
mouthful - so let's free up the String name by renaming the existing
class.
Making the old one have an annoying name will hopefully also help with
quick adoption :^)
Previously only a QOI image decoder was available on the system. This
commit adds an encoder as well.
For now it only handles images with 4 channels (RGBA).
