patch 8.2.0158: triggering CompleteDone earlier is not backwards compatible

Problem:    Triggering CompleteDone earlier is not backwards compatible.
            (Daniel Hahler)
Solution:   Add CompleteDonePre instead.
diff --git a/src/vim.h b/src/vim.h
index 9402c4e..23e5374 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -1303,6 +1303,7 @@
     EVENT_COLORSCHEMEPRE,	// before loading a colorscheme
     EVENT_COMPLETECHANGED,	// after completion popup menu changed
     EVENT_COMPLETEDONE,		// after finishing insert complete
+    EVENT_COMPLETEDONEPRE,	// idem, before clearing info
     EVENT_CURSORHOLD,		// cursor in same position for a while
     EVENT_CURSORHOLDI,		// idem, in Insert mode
     EVENT_CURSORMOVED,		// cursor was moved