OpenSystemsDevelopment / qpdf

Also,
- use Pl_Discard when only checking whether stream is filterable
- get last char directly from output string

Fix parsing of object streams containing objects with no white-space between them

... 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.

Refactor calls to QPDFParser::parse

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

Make all non-static methods including constructors private.

Refactor QPDF::resolveObjectsInStream

Only build strings when needed.

... to QPDFObjectHandle_private.hh

Fix object stream error/warning messages reporting wrong object id

This was due to the use of last_object_description, which is not set for
the object stream itself.

Also, modify the messages introduced #1391 and #1392 to report the supposed
offset of the objects.

Refactor writing of object streams

Cache output of pass 1.

Fix #1394

Move methods responsible for loading or keeping track of objects to
QPDF_objects.cc.

The split was part of the reverted #1297. Reintroducing it now makes it
easier/safer to keep the work to refactor the xref and object tables in
sync with main.

Also, add reverted #194 to .git-blame-ignore-revs.

This reverts commit bb045907a043b5c6de9fb804ff11087333747329.

Split QPDF.cc into QPDF.cc and QPDF_objects.cc

Move methods responsible for loading or keeping track of objects to
QPDF_objects.cc.

The split was part of the reverted #1297. Reintroducing it now makes it
easier/safer to keep the work to refactor the xref and object tables in
sync with main.

Refine recovery from missing startxref (fixes #1335)

Refactor xref table reconstruction (Fixes #1362)

Refactor InputSource

linearization parameter dictionary.

Spec states that that linearization parameter dictionary must be the first
object.

Improve support for reading into std::string objects.

Move qpdf private inline methods to private header file.

Minor code tidy and update .git-blame-ignore-revs

Ignore reverted #1272, #1289, #1297 and #1301.
Ignore last two commits.

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