OpenSystemsDevelopment / qpdf

Replace most of the calls to QUtil::copy_string with this instead.

This is a massive rewrite of the help text and cli.rst section of the
manual. All command-line flags now have their own help and are
specifically index. qpdf --help is completely redone.

Handle optional choices in addition to required choices. Refactor the
way help options are added to completion to make it work with optional
help choices.

* Make it a runtime error, not a logic error
* Include additional information
* Capture it properly in checkLinearization

Create a computationally and memory efficient implementation of name
and number trees that does binary searches as intended by the data
structure rather than loading into a map, which can use a great deal
of memory and can be very slow.

If QPDF_CRYPTO_PROVIDER is set, just run the tests for the given
provider. This is to support cases of running the entire test suite
for each provider. If QPDF_CRYPTO_PROVIDER is not set, run the tests
that exercise the cyrpto provider for each available provider.

This code was essentially duplicated between test_driver and
standalone_fuzz_target_runner.

Have classes contain only a single private member of type
PointerHolder<Members>. This makes it safe to change the structure of
the Members class without breaking binary compatibility. Many of the
classes already follow this pattern quite successfully. This brings in
the rest of the class that are part of the public API.

This makes all integer type conversions that have potential data loss
explicit with calls that do range checks and raise an exception. After
this commit, qpdf builds with no warnings when -Wsign-conversion
-Wconversion is used with gcc or clang or when -W3 -Wd4800 is used
with MSVC. This significantly reduces the likelihood of potential
crashes from bogus integer values.

There are some parts of the code that take int when they should take
size_t or an offset. Such places would make qpdf not support files
with more than 2^31 of something that usually wouldn't be so large. In
the event that such a file shows up and is valid, at least qpdf would
raise an error in the right spot so the issue could be legitimately
addressed rather than failing in some weird way because of a silent
overflow condition.