Fix various file descritor, and memory leaks in ArArchive, DebFile,
and TagFile by introducing a new PyApt_UniqueObject smart pointer
that is like a unique_ptr, but backportable to older releases, and
automatically clears subobjects, so objects with cycles like DebFile
and TagFile will be released on error paths.

LP: #1899193
GHSL-2020-170
CVE-2020-27351