OpenSystemsDevelopment / qpdf

Removed `expand_filter_name` method and integrated its functionality directly into `filter_factory` for improved clarity and maintainability. Consolidated filter handling logic to eliminate redundant operations and streamline code execution.

Replaced individual compression flags with a unified decode-level parameter for stream filtering. Introduced a helper function to handle filtering conditions, reducing redundancy and improving readability. Removed unused code and updated related tests to reflect these changes.

Moved `anyBadTokens` and `lastTokenWasBad` methods to inline definitions within the header file for improved readability and maintainability. Also marked the class and relevant methods as `final` to prevent further inheritance and overrides.

Moved stream filter factory logic into `Members::filter_factory` for better encapsulation and maintainability. Removed redundant static filter factory map and improved error handling for invalid stream filter configurations.

Moved the filter abbreviation expansion logic from a static map to a new `expand_filter_name` method in `QPDF_Stream::Members`. This simplifies the code, improves maintainability, and consolidates the logic for easier testing and updates.

Reject objects containing arrays or dictionaries with more than 5000
elements. We are by definition dealing with damaged files, and such
objects are extremely likely to be invalid or malicious.

Thanks to github user @cdosborn for the basic enhancement.

Only top-level XMP metadata is supposed to be left unencrypted. All
other metadata is not treated specially.

Rather than converting each (sequential) object id to a string,
generate a string for the first id and than increment the digits in the
string.

... to remove the /Root /StructTreeRoot and /MarkInfo entries.

... and use it in QPDFWriter and QPDF::generateHintStream.

... containing objects with no white-space between them.

To enforce the rule that objects end at the start-offset of the next
object, each object is parsed in it own object stream.

To facilitate this, a new private API input source is::OffsetBuffer has
been added which only contains the object but reports offsets relative to
the start of the object stream. This is adapted from OffsetInputSource by
changing the direction of the offset, endowing it with its own
BufferInputSource and striooing out checks duplicated in BufferInputSource.

Fixes the expected failure in the test case added in #1266.

Add static parse methods. Make all external access to QPDFParser through
static methods.

Make all non-static methods including constructors private.

Only build strings when needed.

... to QPDFObjectHandle_private.hh

Improve support for reading into std::string objects.

Move qpdf private inline methods to private header file.

- Add missing export for operator QPDFObjGen.

- Fix handling of indirect references. The use of the type_code method
  in various switch statements bypassed the special handling of
  ::ot_reference objects. Replace with new method resolved_type_code.

Add tests for ::ot_reference objects.

Avoid creating new identical descriptions for each content stream token.

Also remove some shared pointers and use std::string instead of Pl_Buffer
in Pl_QPDFTokenizer.

Modernise constructors, make classes final, etc.

Remove remaining QPDFTokenizer private methods.
Remove QPDFTokenizer privileged access to Tokenizer.

Add new private Util.hh header to define inline functions and expose as
ordinary functions in QUtil.