Individualize NameHashSet Hashing & Revisit #709 (#740)

* Make mac/win lookups lowercase'd

* Revert #709 & 81042cc

* Adjust HashPolicy implementation across sourcemod

Basically, in order to implement our own (actual) hash policy in
`PluginSys.h`, we needed to remove the blanket implementation of `hash`
that was used before. Now, each policy must implement `hash` along with
`matches` in order to be used with `NameHashSet`. While this does force
us to change every implementation of policies across the entirety of
sourcemod, it allows core to use flexible implementations of `hash`.

* Remove logic duplication

* Improve lowercase checks

extensions/topmenus/TopMenu.h

@@ -77,6 +77,10 @@ struct topmenu_object_t
 	{
 		return strcmp(name, topmenu->name) == 0;
 	}
+	static inline uint32_t hash(const detail::CharsAndLength &key)
+	{
+		return key.hash();
+	}
 };
 
 struct topmenu_category_t