mPDF set logger

This logs mPDF messages. It includes debug logging too, which is less desirable.

I could create a custom wrapper class, which would not log debug messages. At some later date the logging level could be configured on the settings form, ✨ Should mpdf render using \Mpdf\HTMLParserMode::HTML_BODY Needs work

Updated MR and used DI to use logger service, thanks!

Rebased with latest changes from 2.x.

I updated the logger to 'logger.channel.pdf_api' to match the logger in DomPdf.

Automatically closed - issue fixed for 2 weeks with no activity.