Initially some proof of concept code was implemented here, but then I
copied that to VCL and it got fixes there, so call into vcl from here
instead of invoking pdfium directly.

Change-Id: I8590cbe94876ff6aff3f870535a99062304f3996
Reviewed-on: https://gerrit.libreoffice.org/37016Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>