OpenSystemsDevelopment / qpdf

Refine recovery from missing startxref (fixes #1335)

Refactor xref table reconstruction (Fixes #1362)

Improve support for reading into std::string objects.

Move qpdf private inline methods to private header file.

If startxref cannot be found in the last 1024 try finding it in the
whole file and check whether it is valid.

Split reconstruction into three passes - scanning of input for objects and
trailer, insertion of objects into the xref table, and loading the trailer.

This allows insertion to take place in the usual reverse order and removes
the need for a separate insertReconstructedXrefEntry method.

It also allows trailer to be tried from most recent to oldest.

Ignore any found trailers without /Root entry.

There simply is no chance Members will be required during the life of
qpdf 12.

...and include ObjectHandle.hh first in QPDFObjectHandle so there is
at least one place (other than check_abi get-sizes) that includes it
first.

- 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.

Enhance error checking of object stream object ids and offsets

The original test file contains multiple entries with id 0 and offset 0.
One entry has been modified such that the id is valid (6).

Object streams with invalid offsets are a source of unreproduceable
oss-fuzz time-outs.

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

Update release notes and reverse making QPDFObjectHandle final

and delay to qpdf 13 to give users notice of the change.

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.

- Remove unnecessary QPDF_DLLs
- make deleted constructors public
- move some comments to support tooltips
- modernise some constructors and destructors
- change some member shared pointers to unique pointers

Clean up comments in QPDFObject.hh

Move all stream-specific methods to new class qpdf::Stream

Move all array-specific methods to new class qpdf::Array.

Move all dictionary specific methods to BaseDictionary. Create new subclass
Dictionary to allow QPDFObjectHandle to access the moved methods.