vim:keys: Add visual equivalent of substitute maps

.config/vim/vimrc.d/40-keys.vim

@@ -242,9 +242,11 @@ noremap ][ ]]
 
 " Strip trailing whitespace
 nnoremap <leader><space> :silent! %s/\v\s+$//<CR>
+vnoremap <leader><space> :<C-u>silent! '<,'>s/\v\s+$//<CR>
 
 " Convert double quotes to single
 nnoremap <leader>" :silent! %s/"/'/g<CR>
+vnoremap <leader>" :<C-u>silent! '<,'>s/"/'/g<CR>
 
 " Keep selection when changing the indentation in visual mode
 vnoremap > >gv