Update dompdf to v3

There's a security advisory out so we probably should be looking to move that way, it would require a new major.

During my last normal Drupal core update, composer detected that dompdf has security advisories and blocked the whole upgrade/install.

The patch here seems correct, but since this patch here runs POST composer check, it would not solve it the install problem. To really get this to work, it has to become part of the next release.

To circumvent the problem for now, and actually load up the 3+ version of dompdf, I did this:
$ composer require "dompdf/dompdf:3.1.6 as 2.0.8" --update-with-all-dependencies

@nojj did adding <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/> solve your issue with special characters?

will be released to v3