patch 8.2.4400: MS-Windows: cannot use the mouse in the console with VIMDLL

Problem:    MS-Windows: cannot use the mouse in the console with VIMDLL.
Solution:   use add_char2buf() instead of fix_input_buffer(). (closes #9784,
            closes #9769)
diff --git a/src/getchar.c b/src/getchar.c
index 8513679..7a1ef8c 100644
--- a/src/getchar.c
+++ b/src/getchar.c
@@ -1138,18 +1138,9 @@
     }
     else
     {
-	char_u	*p = buf + len;
-	int	char_len = (*mb_char2bytes)(c, p);
-#ifdef FEAT_GUI
-	int	save_gui_in_use = gui.in_use;
-
-	gui.in_use = FALSE;
-#endif
-	// if the character contains CSI or K_SPECIAL bytes they need escaping
-	len += fix_input_buffer(p, char_len);
-#ifdef FEAT_GUI
-	gui.in_use = save_gui_in_use;
-#endif
+	char_u *end = add_char2buf(c, buf + len);
+	*end = NUL;
+	len = end - buf;
     }
     (void)ins_typebuf(buf, KeyNoremap, 0, !KeyTyped, cmd_silent);
     return len;
@@ -3671,7 +3662,9 @@
 	    p += 2;
 	    i -= 2;
 	}
-	// When the GUI is not used CSI needs to be escaped.
+# ifndef MSWIN
+	// When not on MS-Windows and the GUI is not used CSI needs to be
+	// escaped.
 	else if (!gui.in_use && p[0] == CSI)
 	{
 	    mch_memmove(p + 3, p + 1, (size_t)i);
@@ -3680,6 +3673,7 @@
 	    *p = (int)KE_CSI;
 	    len += 2;
 	}
+# endif
 	else
 #endif
 	if (p[0] == NUL || (p[0] == K_SPECIAL