OpenSystemsDevelopment / qpdf

…s for consistency with refactored AcroForm structure.

…ion and leveraging shared components.

- Modify `traverseField` to return `bool` for identifying invalid fields.
- Add `bad_fields` set to track and handle problematic fields.
- Improve error handling for invalid parent entries.

… for clarity and consistency across dictionary operations.

…ent and simplified temporary null management. Clean up unused test coverage markers.

…t` consistency to handle invalid entries, and improve loop detection logic.

…` parameter, update conditional checks, and streamline logic for field and annotation handling.

Tighten validation of the PDF spec requirements that form fields form a tree and that widget annotations have a single parent by utilizing `field_to` and `annotation_to_field` in the loop detection check.

Replace direct access to document helpers (`acroform()`, `pages()`, `embedded_files()`, etc.) with calls through `QPDF::doc()` for better encapsulation. Adjust related methods, constructors, and memory management accordingly.

… redundant `initialized_dr_map` flag and directly checking `dr`.

…g with `Dictionary` and `Array`.

… with `std::deque` in `traverse_field` for better performance and simplify traversal logic.

…ield` function to increase code clarity.

…h `std::list<Dictionary>`, simplify `/Kids` handling, and update method calls for consistency.

…annotation` to increase code clarity.

…h operator[], update type handling for clarity and consistency, and streamline resource merging.

…roFormDocumentHelper`, replace redundant maps with `FieldData` encapsulation.

…n `QPDFOutlineObjectHelper` and `QPDFOutlineDocumentHelper`.

…n `QPDFAcroFormDocumentHelper`.

…e memory management, and streamline class definition.

…e()` for re-validation and repair of AcroForm structure.

…roduce `empty` checks, and use `std::cmp_less` and `emplace_back` for better clarity and efficiency.

…`warn`, streamline condition handling.

Refactored several classes to use C++11 `final` specifiers for inheritance restrictions and added default member initializations. These changes enhance code clarity, improve safety, and ensure modern coding practices.

Simplified checks for empty containers and strings across the codebase using the `.empty()` method. This improves code readability and adheres to best practices for checking emptiness.

Converted multiple occurrences of `count()` to `contains()` throughout the codebase where the goal was to check key existence in containers. This improves code readability and aligns with modern C++ practices, particularly with C++20, making the intent more explicit and potentially aiding performance.

This improves indentation of long strings. This commit also fixes some
trailing whitespace in ChangeLog.

Rather than adding yet another flag that is almost never useful on its
own, just have --remove-restrictions disable digital signatures. The
operations are still separate in the API.