The reviewboard build backend writes out a package-dependencies.txt file as part of most operations. This was including package_only_dependencies all the time, which cause editable installs to fail now that the rbintegrations dependency has been bumped to an unreleased dev version. This change makes it so when we write out the dependencies file, we only include those if we're building a wheel or sdist. While in here, I fixed a couple small docstring issues and added `_write_dependencies()` calls to a few additional methods, in case the build backend ends up calling them in isolation without first calling some of the other methods. Testing Done: Did an editable install and saw that it worked.