Add :vc keyword to use-package for VC package support

Add :vc keyword to use-package for VC package support

* lisp/use-package/use-package-core.el (use-package-keywords): Add :vc.
(use-package-handler/:load-path): Insert 'load-path' into 'state'.
(use-package-vc-install): Install the package with package-vc.el.
(use-package-handler/:vc): Handler for the :vc keyword.
(use-package-normalize--vc-arg): Normalization for more complex
arguments to 'use-package-normalize/:vc', in order to make them
compatible with the specification of 'package-vc-selected-packages'.
(use-package-normalize/:vc): Normalizer for the :vc keyword.
(use-package): Document :vc.
* lisp/use-package/use-package-ensure.el (use-package-handler/:ensure):
Do not ensure a package when :vc is used in the declaration.
* test/lisp/use-package/use-package-tests.el (use-package-test/:vc-1):
(use-package-test/:vc-2):
(use-package-test/:vc-3):
(use-package-test/:vc-4):
(use-package-test/:vc-5):
(use-package-test-normalize/:vc):
Add tests for :vc.
* etc/NEWS: Mention change.  (Bug#60418)