* lisp/eshell/esh-cmd.el (eshell-post-rewrite-command-function): New var.

* lisp/eshell/esh-cmd.el (eshell-post-rewrite-command-function): New var.
(eshell-post-rewrite-command-hook): Make obsolete.
(eshell-parse-command): Simplify.
(eshell-structure-basic-command): Remove unused arg `vocal-test'.
(eshell--cmd): Declare.
(eshell-parse-pipeline): Remove unused var `final-p'.
Pass a dynvar to eshell-post-rewrite-command-hook.
Implement the new eshell-post-rewrite-command-function.
(eshell-invoke-directly): Remove unused arg `input'.
* lisp/eshell/esh-io.el (eshell-io-initialize):
Use eshell-post-rewrite-command-function.
(eshell--apply-redirections): Rename from eshell-apply-redirections;
adjust to new calling convention.
(eshell-create-handles): Rename args to avoid clashing with dynvar
`standard-output'.

Fixes: debbugs:15399