Make emacs prefer an existing ~/.emacs.d to an existing XDG location

Make emacs prefer an existing ~/.emacs.d to an existing XDG location

* doc/emacs/custom.texi (Find Init): Update description of how Emacs
finds its init file directory and the interaction with
$XDG_CONFIG_HOME
(Early Init File): Correct XDG location of early-init.el

* etc/NEWS: Update description to make it clear the ~/.emacs.d is
preferred, even if the XDG location exists.

* lisp/startup.el: Prefer ~/.emacs.d even if the XDG location exists.

* lib-src/emacsclient.c (open_config): Prefer home directory the XDG
location.