patch 8.0.0893: cannot get the scroll count of a terminal window

Problem:    Cannot get the scroll count of a terminal window.
Solution:   Add term_getscrolled().

src/terminal.c

@@ -40,14 +40,15 @@
  *   - Need an option or argument to drop the window+buffer right away, to be
  *     used for a shell or Vim. 'termfinish'; "close", "open" (open window when
  *     job finishes).
+ *     patch by Yasuhiro: #1950
  * - add option values to the command:
  *      :term <24x80> <close> vim notes.txt
+ *   or use:
+ *      :term ++24x80 ++close vim notes.txt
  * - support different cursor shapes, colors and attributes
  * - make term_getcursor() return type (none/block/bar/underline) and
  *   attributes (color, blink, etc.)
  * - MS-Windows: no redraw for 'updatetime'  #1915
- * - term_getline() and term_scrape() don't work once the job exited. Use the
- *   buffer and scrollback, remembering the topline from when the job exited.
  * - To set BS correctly, check get_stty(); Pass the fd of the pty.
  *   For the GUI fill termios with default values, perhaps like pangoterm:
  *   http://bazaar.launchpad.net/~leonerd/pangoterm/trunk/view/head:/main.c#L134
@@ -2025,6 +2026,19 @@ f_term_getline(typval_T *argvars, typval_T *rettv)
     }
 }
 
+/*
+ * "term_getscrolled(buf)" function
+ */
+    void
+f_term_getscrolled(typval_T *argvars, typval_T *rettv)
+{
+    buf_T	*buf = term_get_buf(argvars);
+
+    if (buf == NULL)
+	return;
+    rettv->vval.v_number = buf->b_term->tl_scrollback_scrolled;
+}
+
 /*
  * "term_getsize(buf)" function
  */