defaults: 'showcmd', 'belloff', 'ruler'

- Vim "unix default" of 'noshowcmd' is serving few users. And it's
  inconsistent.
- 'ruler' and 'belloff=all' improve the out-of-the-box experience.
- Continue to use 'noshowcmd' and 'noruler' by default in the functional
  tests to keep them fast.

TODO: Add a "disable slow stuff" command or mapping to address the
use-case of a very slow terminal connection.

src/nvim/testdir/setup.vim

@@ -1,5 +1,9 @@
 " Common preparations for running tests.
 
+set noruler
+set noshowcmd
+set belloff=
+
 " Make sure 'runtimepath' does not include $HOME.
 set rtp=$VIM/vimfiles,$VIMRUNTIME,$VIM/vimfiles/after