Yup - You are on the right track
Considering your show of humility, I will tell you what the problem is:
You can't just dump in a php.ini file from a different installation into a 'suite' setup such as XAMMP or WAMP.
And that error is 'what the problem' is - you can't transplant things. The mysqli that is called is the one that would work with a different compilation of PHP.
That's how I found the problem - I looked in your php.ini for the 'unloadable' extension (from your first post) extension=php_mysqli.dll
Then I searched/compared the original XAMPP php.ini - that extension is NOT present. Then I looked at the structure of the php.ini and knew it came from a different installation. The XAMPP php.ini calls: extension=php_mysqli_libmysql.dll
The PHP.INI you have in there is calling the wrong libraries (DLLs).
Replace it with the original XAMMP php.ini -- then make changes. DON'T try to patch things -- you will only discover other errors, or worse - you will discover them when things are working, you add a new routine and it fails when you activate an extension.
You can't mix and match parts -- enough said.