major: Switch to forward slashes(+more) to fix compilation on Linux (#1403)

Notably also adds some metadata files for NixOS 

* add support for linux clang cross compiles

* add linux clang instructions

* un-capitalize Mob.horse.*

* update the description in flake.nix

---------

Co-authored-by: Loki <lokirautio@gmail.com>

Minecraft.Client/Orbis/Network/Orbis_NPToolkit.cpp

@@ -1,7 +1,7 @@
 #include "stdafx.h"
 
 #include "Orbis_NPToolkit.h"
-#include "Orbis\ps4__np_conf.h"
+#include "Orbis/ps4__np_conf.h"
 #include "Orbis/Network/SonyCommerce_Orbis.h"
 
 // #define NP_TITLE_ID "CUSA00265_00"

Minecraft.Client/Orbis/Network/SQRNetworkManager_Orbis.cpp

@@ -12,9 +12,9 @@
 #include "../ps4__np_conf.h"
 #include "Orbis_NPToolkit.h"
 #include "SonyVoiceChat_Orbis.h"
-#include "Common\Network\Sony\SonyHttp.h"
-#include "..\..\..\Minecraft.World\C4JThread.h"
-// #include "..\PS3Extras\PS3Strings.h"
+#include "Common/Network/Sony/SonyHttp.h"
+#include "../../../Minecraft.World/C4JThread.h"
+// #include "../PS3Extras/PS3Strings.h"
 
 
 int (* SQRNetworkManager_Orbis::s_SignInCompleteCallbackFn)(void *pParam, bool bContinue, int pad) = nullptr;

Minecraft.Client/Orbis/Network/SQRNetworkManager_Orbis.h

@@ -8,7 +8,7 @@
 #include <unordered_map>
 // #include "SonyVoiceChat_Orbis.h"
 
-#include "..\..\Common\Network\Sony\SQRNetworkManager.h"
+#include "../../Common/Network/Sony/SQRNetworkManager.h"
 
 class SQRNetworkPlayer;
 class ISQRNetworkManagerListener;

Minecraft.Client/Orbis/Network/SonyCommerce_Orbis.cpp

@@ -1,7 +1,7 @@
 #include "stdafx.h"
 
 #include "SonyCommerce_Orbis.h"
-#include "PS3\PS3Extras\ShutdownManager.h"
+#include "PS3/PS3Extras/ShutdownManager.h"
 #include <sys/event.h>
 
 

Minecraft.Client/Orbis/Network/SonyCommerce_Orbis.h

@@ -1,6 +1,6 @@
 #pragma once
 
-#include "Common\Network\Sony\SonyCommerce.h"
+#include "Common/Network/Sony/SonyCommerce.h"
 class OrbisNPToolkit;
 	
 class SonyCommerce_Orbis : public SonyCommerce

Minecraft.Client/Orbis/Network/SonyRemoteStorage_Orbis.h

@@ -1,7 +1,7 @@
 #pragma once 
 
 
-#include "Common\Network\Sony\SonyRemoteStorage.h"
+#include "Common/Network/Sony/SonyRemoteStorage.h"
 
 class SonyRemoteStorage_Orbis : public SonyRemoteStorage
 {