AK+LibCompress: Remove the Deflate back-reference intermediate buffer

Instead of reading bytes from the output stream into a buffer, just to
immediately write them back out, we can skip the middle-man and copy the
bytes directly into the output buffer.

AK/CircularBuffer.cpp

@@ -206,4 +206,20 @@ ErrorOr<size_t> CircularBuffer::fill_from_stream(Stream& stream)
     return bytes.size();
 }
 
+ErrorOr<void> CircularBuffer::copy_from_seekback(size_t distance, size_t length)
+{
+    if (distance > m_seekback_limit)
+        return Error::from_string_literal("Tried a seekback copy beyond the seekback limit");
+
+    while (length > 0) {
+        auto next_span = next_read_span_with_seekback(distance);
+        if (next_span.size() == 0)
+            break;
+
+        length -= write(next_span.trim(length));
+    }
+
+    return {};
+}
+
 }