I am using PHP-CS-Fixer and I have .php_cs.dist file in my workspace. It's something like this:

<?php

return PhpCsFixer\Config::create()
    ->setRiskyAllowed(true)
    ->setRules([
    ...
    ])
;

I have added file association:

"files.associations": {
    ".php_cs.dist": "php",
    ...
},

PHP-CS-Fixer is installed globally, so this library is not in my vendor directory, therefore intelephense shows an error when cursor is on PhpCsFixer\Config: Undefined type 'PhpCsFixer\Config'.intelephense(1009).

To get rid of this error, I have added intelephense.environment.includePaths entry:

"intelephense.environment.includePaths": [
    "/Users/username/.composer/vendor/friendsofphp/php-cs-fixer/src"
],

Unfortunately it doesn't work (tried reloading window, reloading vscode, reindexing workspace). Error still occurs. Path is valid, class file exists, namespace is valid.
Everything is fine when PHP-CS-Fixer is installed internally (inside local vendor directory).