'C-1 C-x v L' asks for revision and shows its log entry with diff (bug#38044)

'C-1 C-x v L' asks for revision and shows its log entry with diff (bug#38044)

* doc/emacs/maintaining.texi (VC Change Log): Explain the numeric prefix arg
of 'C-x v L' (vc-print-root-log).

* lisp/vc/vc-git.el (vc-git-print-log): Add command line option "-p"
when vc-log-view-type is 'with-diff'.
(vc-git-log-view-mode): Use long style when vc-log-view-type is 'with-diff'.

* lisp/vc/vc.el (vc-print-log-internal): Add optional arg 'type'.
(vc-log-internal-common): Use 'region-history-mode' when type is
'with-diff' and backend supports 'region-history-mode'.
(vc-print-root-log): Add optional arg 'revision'.  In interactive spec
read a revision when current-prefix-arg is 1.  Use current-prefix-arg
"as is" when it is a number.  Show revision in long style with diff
when limit is 1 and revision is non-nil.