feat(nvim): add vim-sort-motion

Re-add a plugin to add a text object and motion to sort lines. This
means I can run commands like `gsip` to sort lines within a paragraph
without needing to select them first.

https://github.com/christoomey/vim-sort-motion

system/shared/home-manager.nix

@@ -519,6 +519,7 @@ in
       vimPlugins.vim-polyglot
       vimPlugins.vim-repeat
       vimPlugins.vim-sleuth
+      vimPlugins.vim-sort-motion
       vimPlugins.vim-surround
       vimPlugins.vim-terraform
       vimPlugins.vim-test