Use `org-show-entry' for `org-inlinetask-toggle-visibility'.

* org-inlinetask.el (org-inlinetask-toggle-visibility): Use
`org-show-entry' instead of `outline-flag-region' to keep the
drawers folded when unfolding an inline task.

Thanks to Viktor Rosenfeld for requiring this.

lisp/org-inlinetask.el

@@ -454,7 +454,7 @@ Either remove headline and meta data, or do special formatting."
      ((= end start))
      ;; Inlinetask was folded: expand it.
      ((get-char-property (1+ start) 'invisible)
-      (outline-flag-region start end nil))
+      (org-show-entry))
      (t (outline-flag-region start end t)))))
 
 (defun org-inlinetask-remove-END-maybe ()