OpenSystemsDevelopment / qpdf

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.

I always think of doing this after I have already tagged the release.

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

Figuring out which classes are part of the public API by using library
symbols is fragile (dependent on specific compiler optimizations) and
unreliable (misses some inline things). Instead, use castxml, a tool
that parses C++ to an abstract syntax tree and generates XML, to get a
reliable accounting of public classes and their sizes.

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

Use BaseHandle::operator QPDFObjGen in examples

Fix two BaseHandle bugs

- 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.

Deprecate QPDFObjectHandle::parse overload and undeprecate isInitialized

Use Tokenizer instead of QPDFTokenizer internally in qpdf

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.

Update release notes and reverse making QPDFObjectHandle final

Move QPDFObject::copy, disconnect, unparse and write_json to BaseHandle

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

Refactor QPDFTokenizer

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

Tidy public header files