LibJS: Fix incorrect token column values (#2401)

- initializing m_line_column to 1 in the lexer results in incorrect
  column values in tokens on the first line of input.
- not incrementing m_line_column when EOF is reached results in
  an incorrect column value on the last token.

Libraries/LibJS/MarkupGenerator.cpp

@@ -43,9 +43,7 @@ String MarkupGenerator::html_from_source(const StringView& source)
     auto lexer = Lexer(source);
     for (auto token = lexer.next(); token.type() != TokenType::Eof; token = lexer.next()) {
         auto length = token.value().length();
-        auto start = token.line_column();
-        // FIXME: Why do we need to do this magic math? This math isn't even accurate enough, code like "let x = 10" renders incorrectly.
-        start = start < 2 ? 0 : start - 2;
+        auto start = token.line_column() - 1;
 
         if (start > source_cursor) {
             builder.append(source.substring_view(source_cursor, start - source_cursor));
@@ -321,4 +319,4 @@ String MarkupGenerator::wrap_string_in_style(String source, StyleType type)
     return String::format("<span style=\"%s\">%s</span>", style_from_style_type(type).characters(), source.characters());
 }
 
-}
+}