LibPDF: Add a comment that PDF 2.0 added a length key for inline images

In practice, basically no file has it, since it was only added in 2.0,
and 1.7 explicitly said "in particular, the Type, Subtype, and Length
entries normally found in a stream or image dictionary are unnecessary."

Userland/Libraries/LibPDF/Parser.cpp

@@ -559,6 +559,7 @@ PDFErrorOr<Vector<Operator>> Parser::parse_operators()
                 // FIXME: Check for ASCIIHexDecode and ASCII85Decode.
                 m_reader.consume(1);
 
+                // FIMXE: PDF 2.0 added support for `/L` / `/Length` in inline image dicts. If that's present, we don't have to scan for `EI`.
                 while (!m_reader.done()) {
                     // FIXME: Should we allow EI after matches_delimiter() too?
                     bool expecting_ei = m_reader.matches_whitespace();