patch 8.2.2922: computing array length is done in various ways

Problem:    Computing array length is done in various ways.
Solution:   Use ARRAY_LENGTH everywhere. (Ken Takata, closes #8305)
diff --git a/src/menu.c b/src/menu.c
index 4f5e26b..fb4be21 100644
--- a/src/menu.c
+++ b/src/menu.c
@@ -73,7 +73,7 @@
     /* 25 */ "Make", "TagJump", "RunCtags", "WinVSplit", "WinMaxWidth",
     /* 30 */ "WinMinWidth", "Exit"
 };
-# define TOOLBAR_NAME_COUNT (sizeof(toolbar_names) / sizeof(char *))
+# define TOOLBAR_NAME_COUNT ARRAY_LENGTH(toolbar_names)
 #endif
 
 /*