Vc-Dir: Use tab and backtab for vc-diff

This makes Vc-Dir a little closer to evil-magit where pressing tab reveals
sections/diffs inline.

evil-collection-vc-dir.el

@@ -42,6 +42,8 @@
 
     "d" 'vc-diff
     "D" 'vc-root-diff
+    "\t" 'vc-diff
+    [backtab] 'vc-root-diff
 
     "R" 'vc-register
     "s" 'vc-register ;; Like `magit-stage'?
@@ -67,10 +69,6 @@
     "u" 'vc-dir-unmark
     "U" 'vc-dir-unmark-all-files
 
-    ;; Movement.
-    "\t" 'vc-dir-next-directory
-    [backtab] 'vc-dir-previous-directory
-
     ;; Rebind paragraph-movement commands.
     "]]" 'vc-dir-next-directory
     "[[" 'vc-dir-previous-directory