Extract some of the logic from the `cpp/missing-check-scanf` query into
the more generally useful `getOutputArgument(int index)`, `getAnOutputArgument()`,
and `getNumberOfOutputArguments()` predicates.
This PR separates the core cpp packs into `codeql/cpp-queries` and
`codeql/cpp-all`.
There are very few lines of code changed. Almost all changes are moving
files around.
