patch 9.1.0704: inserting with a count is inefficient

Problem:  inserting with a count is inefficient
Solution: Disable calculation of the cursor position and topline, if a
          count has been used (Ken Takata)

Optimize insertion when using :normal 10000ix.

This patch optimizes the insertion with a large count (e.g. `:normal
10000ix`).

It seems that calculation of the cursor position for a long line is slow
and it takes O(n^2). Disable the calculation if not needed.

Before:
```
$ time ./vim --clean -c 'normal 10000ix' -cq!
real    0m1.879s
user    0m1.328s
sys     0m0.139s

$ time ./vim --clean -c 'normal 20000ix' -cq!
real    0m5.574s
user    0m5.421s
sys     0m0.093s

$ time ./vim --clean -c 'normal 40000ix' -cq!
real    0m23.588s
user    0m23.187s
sys     0m0.140s
```

After:
```
$ time ./vim --clean -c 'normal 10000ix' -cq!
real    0m0.187s
user    0m0.046s
sys     0m0.093s

$ time ./vim --clean -c 'normal 20000ix' -cq!
real    0m0.217s
user    0m0.046s
sys     0m0.108s

$ time ./vim --clean -c 'normal 40000ix' -cq!
real    0m0.278s
user    0m0.093s
sys     0m0.140s

$ time ./vim --clean -c 'normal 80000ix' -cq!
real    0m0.494s
user    0m0.311s
sys     0m0.140s

$ time ./vim --clean -c 'normal 160000ix' -cq!
real    0m1.302s
user    0m1.140s
sys     0m0.094s
```

closes: #15588

Signed-off-by: K.Takata <kentkt@csc.jp>
Signed-off-by: Christian Brabandt <cb@256bit.org>

Author: k-takata

src/edit.c

@@ -512,6 +512,7 @@ edit(
 #ifdef FEAT_DIFF
 		&& curwin->w_topfill == old_topfill
 #endif
+		&& count <= 1
 		)
 	{
 	    mincol = curwin->w_wcol;
@@ -549,11 +550,13 @@ edit(
 	}
 
 	// May need to adjust w_topline to show the cursor.
-	update_topline();
+	if (count <= 1)
+	    update_topline();
 
 	did_backspace = FALSE;
 
-	validate_cursor();		// may set must_redraw
+	if (count <= 1)
+	    validate_cursor();		// may set must_redraw
 
 	/*
 	 * Redraw the display when no characters are waiting.
@@ -566,7 +569,8 @@ edit(
 
 	if (curwin->w_p_crb)
 	    do_check_cursorbind();
-	update_curswant();
+	if (count <= 1)
+	    update_curswant();
 	old_topline = curwin->w_topline;
 #ifdef FEAT_DIFF
 	old_topfill = curwin->w_topfill;

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    704,
 /**/
     703,
 /**/