OpenSystemsDevelopment / qpdf

Also, fix test cases.

The new method is temporarily an (almost) complete copy of parse, which is
temporarily (almost) unchanged.

Fixes #864. QPDFTokenizer::getValue originally had a std::string_view
return type, which was changed to std::string without removing some
unnecessary string creation.

Stop using nullptr to represent null objects.
Count null array elements and trigger creation of sparse arrays if null count is
greater than 100.

Use move semantics for dictionary creation.

Set parsed offset at the same time as setting description.

Modify QPDFParser::parse to call QPDF::getObject instead.

Also remove no-longer-needed #include

Avoid creating new null objects that later will be discarded and made
implicit.

Part of #729

Part of #729

Part of #729

Replace SparseOHArray with std::vector<QPDFObjectHandle>.

Part of #729

Part of #729

Part of #729

Part of #729