Isolate irrlicht references and use a singleton (#6041)

* Add Device3D class which will contain IrrlichtDevice interface

move getSupportedVideoDrivers to Device3D

Add Device3D singleton & use it in various places

Rename Device3D to Rendering engine & add helper functions to various device pointers

More singleton work

RenderingEngine owns draw_load_screen

move draw functions to RenderingEngine

Reduce IrrlichtDevice exposure and guienvironment

RenderingEngine: Expose get_timer_time() to remove device from guiEngine

Make irrlichtdevice & scene manager less exposed

* Code style fixes

* Move porting::getVideoDriverName, getVideoDriverFriendlyName, getDisplayDensity, getDisplaySize to RenderingEngine

Fix XORG_USED macro -> RenderingEngine + create_engine_device from RenderingEngine constructor directly

* enum paralax => enum parallax

src/guiFormSpecMenu.h

@@ -287,8 +287,7 @@ class GUIFormSpecMenu : public GUIModalMenu
 	};
 
 public:
-	GUIFormSpecMenu(irr::IrrlichtDevice* dev,
-			JoystickController *joystick,
+	GUIFormSpecMenu(JoystickController *joystick,
 			gui::IGUIElement* parent, s32 id,
 			IMenuManager *menumgr,
 			Client *client,
@@ -378,7 +377,6 @@ protected:
 	v2s32 pos_offset;
 	std::stack<v2s32> container_stack;
 
-	irr::IrrlichtDevice* m_device;
 	InventoryManager *m_invmgr;
 	ISimpleTextureSource *m_tsrc;
 	Client *m_client;
@@ -386,7 +384,6 @@ protected:
 	std::string m_formspec_string;
 	InventoryLocation m_current_inventory_location;
 
-
 	std::vector<ListDrawSpec> m_inventorylists;
 	std::vector<ListRingSpec> m_inventory_rings;
 	std::vector<ImageDrawSpec> m_backgrounds;