LibWeb: Emit character/comment tokens lazily to accumulate more data

Instead of emitting data-bearing tokens immediately, do it lazily at
the next state change. This allows us to accumulate full bursts of
text in between tags instead of having one token per character. :^)

Libraries/LibWeb/Parser/HTMLTokenizer.h

@@ -148,6 +148,7 @@ private:
 
     void will_switch_to(State);
     void will_reconsume_in(State);
+    void flush_current_character_or_comment_if_needed();
 
     State m_state { State::Data };
     State m_return_state { State::Data };