nvim: plugin: Add a simple whitespace plugin

Now that we dropped vim-better-whitespace just add something simple to
strip whitespace if we do ever need it.

nvim/.config/nvim/plugin/whitespace.vim

@@ -0,0 +1,12 @@
+" https://vi.stackexchange.com/questions/454/whats-the-simplest-way-to-strip-trailing-whitespace-from-all-lines-in-a-file
+function! Preserve(command)
+  " Preparation: save window state
+  let l:saved_winview = winsaveview()
+  " Run the command:
+  execute a:command
+  " Clean up: restore previous window position
+  call winrestview(l:saved_winview)
+endfunction
+
+nnoremap <unique> <silent> <Leader>ws  :call Preserve("%s/\\s\\+$//e")<CR>
+xnoremap <unique> <silent> <Leader>ws  :call Preserve("%s/\\s\\+$//e")<CR>