Record classes/functions declared as isolated files instead of PSR in composer

[carlosas]

Right now only classes defined by PSR-0 or PSR-4 are extracted from composer.json We should also extract the ones defined by 'files'

"autoload": {
  "files": [
     "src/SomeClass.php",
     "src/functions.php"
  ],
  "psr-4": {
    "Source\\Namespace\\": "FooBar"
  }
}

Reference: https://github.com/carlosas/phpat/issues/159#issuecomment-932731980