patch 8.2.3591: no event is triggered when closing a window

Problem:    No event is triggered when closing a window.
Solution:   Add the WinClosed event. (Naohiro Ono, closes #9110)
diff --git a/src/autocmd.c b/src/autocmd.c
index 1704cd4..14cd4af 100644
--- a/src/autocmd.c
+++ b/src/autocmd.c
@@ -186,6 +186,7 @@
     {"VimLeave",	EVENT_VIMLEAVE},
     {"VimLeavePre",	EVENT_VIMLEAVEPRE},
     {"WinNew",		EVENT_WINNEW},
+    {"WinClosed",	EVENT_WINCLOSED},
     {"WinEnter",	EVENT_WINENTER},
     {"WinLeave",	EVENT_WINLEAVE},
     {"VimResized",	EVENT_VIMRESIZED},
@@ -2042,7 +2043,8 @@
 		|| event == EVENT_OPTIONSET
 		|| event == EVENT_QUICKFIXCMDPOST
 		|| event == EVENT_DIRCHANGED
-		|| event == EVENT_MODECHANGED)
+		|| event == EVENT_MODECHANGED
+		|| event == EVENT_WINCLOSED)
 	{
 	    fname = vim_strsave(fname);
 	    autocmd_fname_full = TRUE; // don't expand it later