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/Libraries/LibGfx/ImageDecoder.h

@@ -47,7 +47,8 @@ protected:
 
 class ImageDecoder : public RefCounted<ImageDecoder> {
 public:
-    static RefPtr<ImageDecoder> try_create(ReadonlyBytes);
+    static RefPtr<ImageDecoder> try_create_for_raw_bytes(ReadonlyBytes);
+    static RefPtr<ImageDecoder> try_create_for_raw_bytes_with_known_path(StringView path, ReadonlyBytes);
     ~ImageDecoder() = default;
 
     IntSize size() const { return m_plugin->size(); }