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

core/logic/GameConfigs.h

@@ -72,6 +72,10 @@ public: //NameHashSet
 	{
 		return strcmp(key, value->m_File) == 0;
 	}
+	static inline uint32_t hash(const detail::CharsAndLength &key)
+	{
+		return key.hash();
+	}
 private:
 	char m_File[PLATFORM_MAX_PATH];
 	char m_CurFile[PLATFORM_MAX_PATH];