Seldaek

Taken from packagist.org

Packages with a master branch update since June 1st 2018: 98977
Of those, package having requires on PHP extensions: 11676 (11.79%)

As only ~12% of packages declare their extension requirements,
and even then it might not be a complete list, take all this with
a big grain of salt, it is informative but definitely not a
complete picture of the most used extensions.