Preserve point under 'dired-auto-revert-buffer' (third case)

Preserve point under 'dired-auto-revert-buffer' (third case)

* lisp/files.el (find-file): Use pop-to-buffer-same-window
instead of switch-to-buffer.  This preserves Dired window
point when dired-auto-revert-buffer is non-nil.  (Bug#27243)

* test/lisp/dired-tests.el (dired-test-bug27243-01)
(dired-test-bug27243-02, dired-test-bug27243-03): New tests.
The first two replace a previous test that combined them; that
test intermittently fails in the Hydra build system, so maybe
separating the two cases will help locate the point of
failure.  The third test involves find-file but is here
because it, like the others, is testing the effect of
dired-auto-revert-buffer.