I was editing wrong php.ini file in last comment.
Even though loaded configuration path was showing as "D:\wamp64\bin\apache\apache2.4.37\bin\php.ini" inside phpinfo() of WAMP Server, It was actually loading "D:\wamp64\bin\apache\apache2.4.37\bin\phpForApache.ini"
Once I set both the variables inside phpForApache.ini, details are displayed in phpinfo() and error has gone without extra coding line.