patch 9.0.0756: no autocmd event for changing text in a terminal window

Problem:    No autocmd event for changing text in a terminal window.
Solution:   Add TextChangedT. (Shougo Matsushita, closes #11366)
diff --git a/src/terminal.c b/src/terminal.c
index ae532dc..d9f1e0f 100644
--- a/src/terminal.c
+++ b/src/terminal.c
@@ -1222,6 +1222,8 @@
 	setcursor();
     if (redraw)
     {
+	aco_save_T	aco;
+
 	if (term->tl_buffer == curbuf && term->tl_cursor_visible)
 	    cursor_on();
 	out_flush();
@@ -1232,6 +1234,16 @@
 	    gui_mch_flush();
 	}
 #endif
+        // Make sure an invoked autocmd doesn't delete the buffer (and the
+        // terminal) under our fingers.
+	++term->tl_buffer->b_locked;
+
+	// save and restore curwin and curbuf, in case the autocmd changes them
+	aucmd_prepbuf(&aco, curbuf);
+	apply_autocmds(EVENT_TEXTCHANGEDT, NULL, NULL, FALSE, term->tl_buffer);
+	aucmd_restbuf(&aco);
+
+	--term->tl_buffer->b_locked;
     }
 }