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/Common/Network/Sony/NetworkPlayerSony.h

@@ -1,6 +1,6 @@
 #pragma once
 
-#include "..\..\Common\Network\NetworkPlayerInterface.h"
+#include "../../Common/Network/NetworkPlayerInterface.h"
 #include "SQRNetworkPlayer.h"
 
 // This is an implementation of the INetworkPlayer interface, for Sony platforms. It effectively wraps the SQRNetworkPlayer class in a non-platform-specific way.

Minecraft.Client/Common/Network/Sony/PlatformNetworkManagerSony.cpp

@@ -1,9 +1,9 @@
 #include "stdafx.h"
-#include "..\..\..\Minecraft.World\Socket.h"
-#include "..\..\..\Minecraft.World\StringHelpers.h"
+#include "../../../Minecraft.World/Socket.h"
+#include "../../../Minecraft.World/StringHelpers.h"
 #include "PlatformNetworkManagerSony.h"
 #include "NetworkPlayerSony.h"
-#include "..\..\Common\Network\GameNetworkManager.h"
+#include "../../Common/Network/GameNetworkManager.h"
 
 CPlatformNetworkManagerSony *g_pPlatformNetworkManager;
 

Minecraft.Client/Common/Network/Sony/PlatformNetworkManagerSony.h

@@ -1,10 +1,10 @@
 #pragma once
 using namespace std;
 #include <vector>
-#include "..\..\..\Minecraft.World\C4JThread.h"
-#include "..\..\Common\Network\NetworkPlayerInterface.h"
-#include "..\..\Common\Network\PlatformNetworkManagerInterface.h"
-#include "..\..\Common\Network\SessionInfo.h"
+#include "../../../Minecraft.World/C4JThread.h"
+#include "../../Common/Network/NetworkPlayerInterface.h"
+#include "../../Common/Network/PlatformNetworkManagerInterface.h"
+#include "../../Common/Network/SessionInfo.h"
 #include "SQRNetworkPlayer.h"
 
 // This is how often we allow a search for new games

Minecraft.Client/Common/Network/Sony/SQRNetworkManager.h

@@ -12,7 +12,7 @@
 
 #include <unordered_map>
 #if defined __PSVITA__
-#include "..\..\Minecraft.Client\PSVita\4JLibs\inc\4J_Profile.h"
+#include "../../Minecraft.Client/PSVita/4JLibs/inc/4J_Profile.h"
 #endif
 
 class SQRNetworkPlayer;

Minecraft.Client/Common/Network/Sony/SonyCommerce.cpp

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

Minecraft.Client/Common/Network/Sony/SonyHttp.cpp

@@ -3,15 +3,15 @@
 
 
 #ifdef __PS3__
-#include "PS3\Network\SonyHttp_PS3.h"
+#include "PS3/Network/SonyHttp_PS3.h"
 SonyHttp_PS3 g_SonyHttp;
 
 #elif defined __ORBIS__
-#include "Orbis\Network\SonyHttp_Orbis.h"
+#include "Orbis/Network/SonyHttp_Orbis.h"
 SonyHttp_Orbis g_SonyHttp;
 
 #elif defined __PSVITA__
-#include "PSVita\Network\SonyHttp_Vita.h"
+#include "PSVita/Network/SonyHttp_Vita.h"
 SonyHttp_Vita g_SonyHttp;
 
 #endif

Minecraft.Client/Common/Network/Sony/SonyRemoteStorage.h

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