title: Sort packages without adding/updating dependencies
body: <p>On an existing project with a long list of packages and various feature branches where new dependencies are being added I want to mitigate and minimize merge conflicts by adding dependencies in alphabetical order.</p>
  
  <p>To get this cleaned up, though, I'd like to be able to run the <code>--sort-packages</code> functionality on its own -- without adding or updating anything -- as just a single commit that cleans up the existing packages, and then add <code>"sort-packages" : "true"</code> to the <code>"config"</code> section of the composer.json file to ensure all new packages are added in alphabetical order going forward.</p>
  
  <p><strong>Is it possible to sort the packages listed in a messy <code>composer.json</code> file using composer's <code>--sort-packages</code> option on the CLI without actually adding or updating any dependencies?</strong></p>
  
  <p>The only workaround I've found so far is to run composer update some/package --sort-packages  against a package that you're sure wont update because it is already at the latest version. This is not ideal.</p>