**Use case**
`SELECT POSITION('/' IN s) FROM (SELECT 'Hello/World' AS s);`

The same as `position(s, '/')`

if (pos->type != TokenType::OpeningRoundBracket)
            return false;
        ++pos;
        if (ParserKeyword("BOTH").ignore(pos, expected))
        {
            trim_left = true;
            trim_right = true;
            char_override = true;
        }
        else if (ParserKeyword("LEADING").ignore(pos, expected))
        {
            trim_left = true;
            char_override = true;
        }
        else if (ParserKeyword("TRAILING").ignore(pos, expected))
        {
            trim_right = true;
            char_override = true;
        }
        else
        {
            trim_left = true;
            trim_right = true;
        }
        if (char_override)
        {
            if (!ParserExpression().parse(pos, to_remove, expected))
                return false;
            if (!ParserKeyword("FROM").ignore(pos, expected))
                return false;