patch 8.2.1874: can't do something just before leaving Insert mode

Problem:    Can't do something just before leaving Insert mode.
Solution:   Add the InsertLeavePre autocommand event. (closes #7177)
diff --git a/runtime/doc/autocmd.txt b/runtime/doc/autocmd.txt
index 9355d1f..f15cd96 100644
--- a/runtime/doc/autocmd.txt
+++ b/runtime/doc/autocmd.txt
@@ -881,9 +881,14 @@
 				The cursor is restored afterwards.  If you do
 				not want that set |v:char| to a non-empty
 				string.
+							*InsertLeavePre*
+InsertLeavePre			Just before leaving Insert mode.  Also when
+				using CTRL-O |i_CTRL-O|.  Be caseful not to
+				change mode or use `:normal`, it will likely
+				cause trouble.
 							*InsertLeave*
-InsertLeave			When leaving Insert mode.  Also when using
-				CTRL-O |i_CTRL-O|.  But not for |i_CTRL-C|.
+InsertLeave			Just after leaving Insert mode.  Also when
+				using CTRL-O |i_CTRL-O|.  But not for |i_CTRL-C|.
 							*MenuPopup*
 MenuPopup			Just before showing the popup menu (under the
 				right mouse button).  Useful for adjusting the