Improve user experience when extension files not found

Description

(Context: User having issues enabling extensions on PHP on Windows: https://www.reddit.com/r/PHPhelp/comments/1mrxepv/trouble_installing_php_composer_and_laravel/ )

PHP Warning: PHP Startup: Unable to load dynamic library 'curl' (tried: C:\php\ext\curl (The specified module could not be found), C:\php\ext\php_curl.dll (The specified module could not be found)) in Unknown on line 0

I think it would be helpful if this message mentioned the extension_dir setting explicitly.

eg. something along the lines of "Is extension_dir correct?"

If you don't know that this setting exists, it's not obvious why PHP is looking for extension files in the wrong place.

I think it would also help to move the extension_dir setting directly above the extension= list (if possible) in the php.ini template files. (It is mentioned in the comments above, but those are easy to miss)

Inizia individuando il codice che emette l’avviso di avvio della libreria dinamica e i file modello php.ini menzionati nella issue. Controlla come vengono presentati extension_dir e le voci extension, quindi verifica che l’avviso indirizzi esplicitamente gli utenti a extension_dir e che il modello collochi questa impostazione direttamente sopra l’elenco delle estensioni.