Change the call convention for `defvar-keymap'

Change the call convention for `defvar-keymap'

* doc/lispref/keymaps.texi (Changing Key Bindings): Adjust
documentation.

* lisp/simple.el (special-mode-map):
* lisp/net/shr.el (shr-map):
* lisp/net/eww.el (eww-link-keymap):
(eww-mode-map):
(eww-submit-map):
(eww-textarea-map):
(eww-bookmark-mode-map):
(eww-history-mode-map):
(eww-buffers-mode-map):
* lisp/gnus/message.el (message-mode-map):
* lisp/gnus/gnus-html.el (gnus-html-image-map):
* lisp/gnus/gnus-eform.el (gnus-edit-form-mode-map):
* lisp/gnus/gnus-dired.el (gnus-dired-mode-map):
* lisp/gnus/gnus-bookmark.el (gnus-bookmark-bmenu-mode-map):
Adjust usage of `defvar-keymap'.

* lisp/subr.el (define-keymap, define-keymap--define): Change how
these functions call each other.
(defvar-keymap): Change interface to be more like `define-keymap'.

* lisp/emacs-lisp/lisp-mode.el (lisp-indent--defvar-keymap): Remove.
(lisp-indent-function): Don't use it.