LibWeb: Propagate errors from CSS Tokenizer construction

Instead of constructing a Tokenizer and then calling parse() on it, we
now call `Tokenizer::tokenize(...)` directly. (Renamed from `parse()`
because this is a Tokenizer, not a Parser.)

Userland/Libraries/LibWeb/CSS/SyntaxHighlighter/SyntaxHighlighter.cpp

@@ -45,8 +45,7 @@ void SyntaxHighlighter::rehighlight(Palette const& palette)
             false);
     };
 
-    CSS::Parser::Tokenizer tokenizer { text, "utf-8"sv };
-    auto tokens = tokenizer.parse();
+    auto tokens = CSS::Parser::Tokenizer::tokenize(text, "utf-8"sv).release_value_but_fixme_should_propagate_errors();
     for (auto const& token : tokens) {
         if (token.is(Parser::Token::Type::EndOfFile))
             break;