Add new Eshell built-in command 'funcall'

Add new Eshell built-in command 'funcall'

* lisp/eshell/esh-cmd.el (eshell/funcall): New function...

* test/lisp/eshell/em-glob-tests.el (em-glob-test/expand/splice-results)
(em-glob-test/expand/no-splice-results)
(em-glob-test/expand/explicitly-splice-results)
(em-glob-test/expand/explicitly-listify-results):
* test/lisp/eshell/esh-var-tests.el
(esh-var-test/quoted-interp-lisp-indices)
(esh-var-test/quoted-interp-cmd-indices)
(esh-var-test/interp-convert-quoted-var-number)
(esh-var-test/quoted-interp-convert-var-number)
(esh-var-test/quoted-interp-convert-quoted-var-number)
(esh-var-test/last-status-var-lisp-command)
(esh-var-test/last-result-var-split-indices)
(esh-var-test/last-arg-var-split-indices): ... use it in tests.

* doc/misc/eshell.texi (List of Built-ins): Describe this command.