patch 8.1.2219: no autocommand for open window with terminal

Problem:    No autocommand for open window with terminal.
Solution:   Add TerminalWinOpen. (Christian Brabandt)
diff --git a/src/terminal.c b/src/terminal.c
index b50198c..13e32eb 100644
--- a/src/terminal.c
+++ b/src/terminal.c
@@ -690,6 +690,8 @@
     }
 
     apply_autocmds(EVENT_TERMINALOPEN, NULL, NULL, FALSE, newbuf);
+    if (!opt->jo_hidden && !(flags & TERM_START_SYSTEM))
+	apply_autocmds(EVENT_TERMINALWINOPEN, NULL, NULL, FALSE, newbuf);
     return newbuf;
 }