[BUGFIX] Correctly resolve instance script path

Calling a site using http://example.org/index.php/invalid/ leads to
~/index.php/whatever/ being used as internal script path, which causes
errors or internal side-effects.

This behavior seems to occur only on web-servers using Apache with
PHP-CGI or PHP-FPM, using PHP setting `cgi.fix_pathinfo = 1`.

In case `cgi.fix_pathinfo` is enabled, the current script name is
retrieved from `$_SERVER['SCRIPT_FILENAME']` instead.

Resolves: #97543
Releases: main, 11.5, 10.4
Change-Id: Ia5f6b705253d42d4fc409b90b21d0363c4b97974
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74505


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benjamin Franzke <bfr@qbus.de>
Reviewed-by: Benjamin Franzke <bfr@qbus.de>