OpenSystemsDevelopment / qpdf

…t resource handling in `generateTextAppearance`.

…ance`: copy stream data if shared references exceed threshold, ensuring safe updates.

…r replace the appearance stream content with the generated appearance.

…g: ensure checks for dictionary annotations, streamline appearance creation flow, and replace manual key access with methods.

…s for consistency with refactored AcroForm structure.

- Update class name and references in `FormField.hh` and `QPDFFormFieldObjectHelper.cc`.
- Enhance comments to align with PDF specification, providing clearer descriptions of class functionality and attributes.

…th `DV` and `default_value` methods. Simplify logic, improve clarity, and update references.

…lue` for clarity, consistency, and improved readability. Update references and method documentation accordingly.

…streamline logic, update references, and improve method documentation.

…ernativeName`, and `getMappingName` with streamlined implementations using `fully_qualified_name`, `partial_name`, `alternative_name`, and `mapping_name`. Simplify logic and enhance consistency across methods.

…` with `FT` method, streamline logic, and update related references for clarity and consistency.

…le_string` method for clarity, consistency, and improved readability.

…for flexibility and consistency across FormField methods. Adjust related method implementations accordingly.

…ntation, and update references in `FormField` methods.

…consistency, and update QPDFFormFieldObjectHelper accordingly.

… for clarity and consistency across dictionary operations.

…tionary, modernize constructors, and clean up null handling logic.

…up method implementations, and simplify member handling.

…ed_ptr and forward declaration.

…oved shared pointer handling, remove deprecated object methods, and update all references.

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.

…`Dictionary` and `Name` for improved clarity and consistency, and streamline `/Resources` and `/Font` handling.

…s for improved clarity and consistency.

…s in `QPDFFormFieldObjectHelper`.

…ated `acroform()` method and update related references for improved performance, consistency and maintainability.

… validation, improve readability, and reduce redundancy in type checks.

…for improved readability, and remove redundant variables.

…jectHelper`: replace `getArrayNItems` with `size`, simplify array traversal, and centralize `empty` checks for improved clarity and efficiency.

…`warn`, streamline condition handling.

Ensure an appearance stream is not shared  before generating text appearances, improving error handling and data integrity.

Streamlined method definitions, replaced explicit loop counters with range-based loops, and added `final` specifier to class and methods to ensure overriding restrictions. Simplified constructor and member variable initialization.

Simplified code by removing redundant `this` qualifiers where they are not essential, improving readability and alignment with coding standards. No changes were made to functionality.

Return the display value if the choices entry is an array of strings rather
than a single string.

Test file is need-appearances.pdf modified to contain one array entry.

API was defined, but .cc had no implementation. PDF 2.0 manual is surprisingly unclear as to on/off values, giving /Yes in an example and /Off in descriptive text as "not on".