keymap.el: Ease up support for non-`kbd` formats.

keymap.el: Ease up support for non-`kbd` formats.

While we want to standardize on the `kbd` syntax for user-facing code,
the internal vector representation of key sequences is not going away,
so let's not impose silly `key-description + key-parse` roundtrips.
Also, provide some support for packages stuck with user configs defined
to hold old-style key formats.

* lisp/keymap.el (keymap-set): Allow vectors as `key`.
(key-parse-old-format): New function, which stands out better than
`key-description` when searching for uses of the old syntax.

* list/outline.el (outline-minor-mode): Use it.