Reduced complexity and shorten long method

Related to https://scrutinizer-ci.com/g/phpDocumentor/phpDocumentor2/code-structure/develop/operation/phpDocumentor%5CDescriptor%5CFileDescriptor%3A%3AgetAllErrors
Update FileDescriptor.php
take a more descriptive name
Merge pull request #1175 from siad007/patch-21

Reduced complexity and shorten long method