Move package-vc-heuristic-alist and related to vc.el

Move package-vc-heuristic-alist and related to vc.el

* lisp/emacs-lisp/package-vc.el (package-vc--backend-type)
(package-vc-heuristic-alist, package-vc--guess-backend): Rename
to vc-cloneable-backends-custom-type, vc-clone-heuristic-alist
and vc-guess-url-backend respectively, and move to
lisp/vc/vc.el.  Make package-vc-heuristic-alist an obsolete
alias.
(package-vc--clone, package-vc--read-package-name)
(package-vc-install, package-vc-checkout): Use
vc-guess-url-backend.
* lisp/vc/vc.el (vc-cloneable-backends-custom-type)
(vc-clone-heuristic-alist, vc-guess-url-backend): New defconst,
defcustom and defun, respectively: renamed and moved here from
lisp/emacs-lisp/package-vc.el.

(cherry picked from commit 98b02f56d12f2f39a6667d33d50f9e551a267d6d)