We should only rely on LibGfx to decode images for us, if LibGfx
can't decode an image that should be motivation to improve LibGfx,
not hidden by Qt picking up the slack :^)
While it's nice to see <img src="foo.svg"> suddenly work in Ladybird
after linking with the Qt SVG module, this is cheating.
We should implement SVG-as-image ourselves instead of relying on 3rd
party code to do it. :^)
Because TGA images don't have magic bytes as a signature to be detected,
instead assume a sequence of ReadonlyBytes is a possible TGA image only
if we are given a path so we could check the extension of the file and
see if it's a TGA image.
When we know the path of the file being loaded, we will try to first
check its extension, and only if there's no match to a known decoder,
based on simple extension lookup, then we would probe for other formats
as usual with the normal sniffing method.
