Reimplement signature form field and related utility classes in poppler generator
Summary:
This adds class PopplerFormFieldSignature, PopplerSignatureInfo and PopplerCertificateInfo in poppler
generator.
Depends on D14654
Reviewers: aacid
Subscribers: okular-devel
Tags: Okular
Differential Revision: https://phabricator.kde.org/D14655