Is php required to run scripts indepedently from webserver, meaning do we need to run any scripts (such as module installation php scripts or updating php scripts) without starting the webserver?
Can php that is installed in the system be different from the one used from the webserver that comes with apachefriends' xampp?
Is strongly recommended to have PHP as a binary to run scripts, if you ever need to run them.
Yes, the php cli can be different, but must be a version compatible with MediaWiki, and should have the required extensions to run MediaWiki (mbstring, database drivers...)
Thanks for the answer but I am still confused. Which scripts will ever be needed to run from cli? Are those scripts (that must be run from command line), required to run (start, stop, config) the server or are scripts that run from a page inside site, thus can safely use server's php?
If they are required by extensions in order to be installed or to run some kind of modifications or for parametrization (outside of the webserver, from command line) then this is an extension's requirement and should be extension's reliability to check if it is safe to run.
Is it sure that there is nothing to worry having a version of php inside server (ex. Apache) and use a second version of php to run (from inside or outside Apache) any script that affects mediawiki site (even if compatible)?
Any script you may need to run are described in Manual:Maintenance scripts. The most usual are update.php during upgrades (although you can use the web installer), and runJobs.php in case you need to manually clear the Manual:job queue, but it may happen that you have a MediaWiki instance running and not have to run a maintenance script on its lifetime.
All php scripts would be run manually (by you), not by extensions.
If you run php on apache as an apache module or as a fpm, it's already a different php binary than the command line binary that would provide your distribution on installation.