LibWeb: Add an optional pointer to an HTMLParser to the HTMLTokenizer

This is needed to access the 'adjusted current node' in the 'Markup
declaration open state'. We don't want to create a full parser for
something like syntax highlighting, so it's optional (null) by default.

Userland/Libraries/LibWeb/HTML/Parser/HTMLParser.cpp

@@ -130,6 +130,7 @@ HTMLParser::HTMLParser(DOM::Document& document, StringView input, const String&
     : m_tokenizer(input, encoding)
     , m_document(document)
 {
+    m_tokenizer.set_parser({}, *this);
     m_document->set_should_invalidate_styles_on_attribute_changes(false);
     auto standardized_encoding = TextCodec::get_standardized_encoding(encoding);
     VERIFY(standardized_encoding.has_value());

Userland/Libraries/LibWeb/HTML/Parser/HTMLTokenizer.h

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -110,6 +111,8 @@ public:
 
     Optional<HTMLToken> next_token();
 
+    void set_parser(Badge<HTMLParser>, HTMLParser& parser) { m_parser = &parser; }
+
     void switch_to(Badge<HTMLParser>, State new_state);
     void switch_to(State new_state)
     {
@@ -151,6 +154,8 @@ private:
     void restore_to(Utf8CodePointIterator const& new_iterator);
     HTMLToken::Position nth_last_position(size_t n = 0);
 
+    HTMLParser* m_parser { nullptr };
+
     State m_state { State::Data };
     State m_return_state { State::Data };