LibGfx+Ladybird+Userland: Don't sniff for TGA images with only raw bytes

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.

Userland/Services/ImageDecoder/ConnectionFromClient.h

@@ -27,6 +27,7 @@ private:
     explicit ConnectionFromClient(NonnullOwnPtr<Core::Stream::LocalSocket>);
 
     virtual Messages::ImageDecoderServer::DecodeImageResponse decode_image(Core::AnonymousBuffer const&) override;
+    virtual Messages::ImageDecoderServer::DecodeImageWithKnownPathResponse decode_image_with_known_path(DeprecatedString const& path, Core::AnonymousBuffer const&) override;
 };
 
 }