Debloat IVideoDriver and IrrlichtDevice includes (#15080)

As the project grows, compile time will not go down unless the header mess
is cleaned up one by one to only include exactly what's needed.

src/client/render/anaglyph.cpp

@@ -20,6 +20,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 
 #include "anaglyph.h"
 #include "client/camera.h"
+#include <IrrlichtDevice.h>
 
 
 /// SetColorMaskStep step

src/client/render/core.h

@@ -21,6 +21,11 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #pragma once
 #include "irrlichttypes_extrabloated.h"
 
+namespace irr
+{
+	class IrrlichtDevice;
+}
+
 class ShadowRenderer;
 class Camera;
 class Client;

src/client/render/pipeline.h

@@ -19,6 +19,8 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #pragma once
 
 #include "irrlichttypes_extrabloated.h"
+#include <IrrlichtDevice.h> // used in all render/*.cpp
+#include <IVideoDriver.h> // used in all render/*.cpp
 
 #include <vector>
 #include <memory>
@@ -31,6 +33,11 @@ class Client;
 class Hud;
 class ShadowRenderer;
 
+namespace irr::video
+{
+	class IRenderTarget;
+}
+
 struct PipelineContext
 {
 	PipelineContext(IrrlichtDevice *_device, Client *_client, Hud *_hud, ShadowRenderer *_shadow_renderer, video::SColor _color, v2u32 _target_size)