More verbose error messages

Problem/Motivation

On verbose mode \Drupal\clamav\Scanner::scan() could report the error more verbosely, e.g. by including the error message from ClamAV.

Steps to reproduce

Proposed resolution

Instead of "The anti-virus scanner could not check the file, so the file cannot be uploaded. Contact the site administrator if this problem persists." the error message could be ""The anti-virus scanner could not check the file, because size limit exceeded, so the file cannot be uploaded. Contact the site administrator if this problem persists."

Remaining tasks

User interface changes

API changes

Data model changes