patch 8.2.4723: the ModeChanged autocmd event is inefficient

Problem:    The ModeChanged autocmd event is inefficient.
Solution:   Avoid allocating memory. (closes #10134)  Rename
            trigger_modechanged() to may_trigger_modechanged().
diff --git a/src/ex_getln.c b/src/ex_getln.c
index 4b14971..3cacf9d 100644
--- a/src/ex_getln.c
+++ b/src/ex_getln.c
@@ -1714,7 +1714,7 @@
     trigger_cmd_autocmd(cmdline_type, EVENT_CMDLINEENTER);
 #ifdef FEAT_EVAL
     if (!debug_mode)
-	trigger_modechanged();
+	may_trigger_modechanged();
 #endif
 
     init_history();
@@ -2555,7 +2555,7 @@
 
 #ifdef FEAT_EVAL
     if (!debug_mode)
-	trigger_modechanged();
+	may_trigger_modechanged();
 #endif
 
 #ifdef HAVE_INPUT_METHOD