Fix "C-u M-!" when 'shell-command-dont-erase-buffer' is non-nil

Fix "C-u M-!" when 'shell-command-dont-erase-buffer' is non-nil

* lisp/simple.el (shell-command-dont-erase-buffer): Clarify the
effect of the various values in the doc string.
(shell-command-save-pos-or-erase, shell-command): Don't move or
push point if the output will go to the current buffer.
(Bug#40690)
(shell-command): Mention 'shell-command-dont-erase-buffer' in the
doc string.

* test/lisp/simple-tests.el
(with-shell-command-dont-erase-buffer): Don't is shell quoting
'like this', as it doesn't work on MS-Windows; quote "like this"
instead.
(simple-tests-shell-command-dont-erase-buffer): Adapt the test to
the new modus operandi.

* doc/emacs/misc.texi (Single Shell): Document the effect of the
various values of 'shell-command-dont-erase-buffer'.

* etc/NEWS: Expand and reword the entry regarding changes in
'shell-command-dont-erase-buffer'.