Fix calling Eshell scripts outside of Eshell

Fix calling Eshell scripts outside of Eshell

* lisp/eshell/em-script.el (eshell-source-file): Make obsolete.
(eshell--source-file): Adapt from 'eshell-source-file'...
(eshell-script-initialize, eshell/source, eshell/.): ... use it.
(eshell-princ-target): New struct.
(eshell-output-object-to-target, eshell-target-line-oriented-p): New
implementations for 'eshell-princ-target'.
(eshell-execute-file, eshell-batch-file): New functions.

* lisp/eshell/esh-mode.el (eshell-mode): Just warn if we can't create
the Eshell directory.

* test/lisp/eshell/em-script-tests.el (em-script-test/execute-file):
(em-script-test/execute-file/args), em-script-test/batch-file): New
tests.

* test/lisp/eshell/eshell-tests-helpers.el (with-temp-eshell-settings):
New function...
(with-temp-eshell): ... use it.

* doc/misc/eshell.texi (Control Flow): Update documentation.

* etc/NEWS: Announce this change (bug#70847).