This follows the pattern for the other services spawned by WebContent.
The notable quirk about this service is that it's actually spawned by
the ImageCodecPlugin rather than in main.cpp in the non-Android port.
As a result we needed to do some ifdef surgery to get all the pieces
in place. But we can now load images in the Android port again :^).
This patch brings a service to handle image decompression. With it comes
security enhancement due to the process boundary. Indeed, consequences
of a potential attack is reduced as only the decoder will crash without
perturbing the WebContent process.
It also allows us to display pages containing images that we claim to
support but still make us crash, like for not-finished-yet decoders.
As an example, we can now load https://jpegxl.info/jxl-art.html without
crashing the WebContent process.
Now that all the classes for Ladybird are in the Ladybird namespace, we
don't need them named as Ladybird::FooBarLadybird. For the Qt-specific
classes, we can tack on a Qt at the end for clarity, but FontPlugin and
ImageCodecPlugin no longer have anything to do with Qt.
