bug#46621: Copy line

[Juri Linkov <juri@linkov.net>]

>> duplicate-line should keep point at the same column.
>
> Ah, yes, that might be nice...

Here is the patch that does this.  So if you have

  foo 1 bar

and need to get

  foo 1 bar
  foo 2 bar
  foo 3 bar
  foo 4 bar
  foo 5 bar

it requires typing the minimal number of keys -
move point to the column with 1, and type:

  C-u <copy-line> 2 <down> 3 <down> 4 <down> 5 <down>

```
diff --git a/lisp/misc.el b/lisp/misc.el
index 28c5d6e07f..57cf8c59ed 100644
--- a/lisp/misc.el
+++ b/lisp/misc.el
@@ -71,13 +71,15 @@ duplicate-line
   (interactive "p")
   (unless n
     (setq n 1))
-  (let ((line (buffer-substring (line-beginning-position) (line-end-position))))
+  (let ((line (buffer-substring (line-beginning-position) (line-end-position)))
+        (column (current-column)))
+    (forward-line 1)
+    (unless (bolp)
+      (insert "\n"))
     (save-excursion
-      (forward-line 1)
-      (unless (bolp)
-        (insert "\n"))
       (dotimes (_ n)
-        (insert line "\n")))))
+        (insert line "\n")))
+    (move-to-column column)))
 
 ;; Variation of `zap-to-char'.
 
```