OpenSystemsDevelopment / qpdf

* Based on feedback, keep gpg as well as cosign for the indefinite
  future
* Streamline release creation process by using the `gh` command-line
  tool (GitHub's official CLI) rather than old-school curl directly
  against the GitHub API, a procedure that predates the `gh` command.

Prepare 12.3.2 release

Fix password handling in QPDFJob to allow multiple specifications and add tests (Fixes #1659)

Fixes #1659

Prepare 12.3.1 release

Add CI test for use of a copy of a destroyed QPDFJob object

Test for #1654

Refactor QPDFJob::Input methods to pass QPDFJob reference

By-pass an issue calling QPDFJob::createQPDF from pikepdf. See https://github.com/pdfarranger/pdfarranger/issues/1312

Reminder in release instructions to mention signer

Refactor QPDFParser

Co-authored-by: m-holger <34626170+m-holger@users.noreply.github.com>

Co-authored-by: m-holger <34626170+m-holger@users.noreply.github.com>

Co-authored-by: m-holger <34626170+m-holger@users.noreply.github.com>

Co-authored-by: m-holger <34626170+m-holger@users.noreply.github.com>

Bump version to 12.3.1

Fix Filename Masks in README-what-to-download.md

Fixes #1648

Minor fixes to release instructions

Allow README change to trigger CI (for 12.3.0)

Virtually all changes are merged through PRs now. The exclusions would
prevent a README change from being the last commit before a release.

Update README for C++20 requirement

Add script to validate private header files in isolation

Introduce `check-private-headers` script to ensure all private headers compile independently. Update `build-linux` script to include this new validation step. Adjust release notes to reflect the additional header checks.

Addresses the issue raised in #1465

Add `--remove-acroform` option to exclude AcroForm dictionary

Introduce a new `--remove-acroform` option to remove the interactive form dictionary from the document catalog. Update related documentation, tests, and release notes to reflect this new feature.

Fixes #1403

Refactor `FormNode::setRadioButtonValue` (fixes #1449)

Fix identification of radio button widgets by relying on the absence of `Kids` arrays.
Fix the exclusion of RadioButtonFields with parents.

Fixes #1449

Update copyrights

Tighten named destination validation in `QPDFOutlineDocumentHelper::r…