PostProcessing: Add native width/height inputs

Available in GLSL as GetNativeSize(), GetUpscaleMultiplier(), and in
reshade as native_width/native_height/upscale_multiplier.

GetPaddedOriginalSize() is now deprecated, as it does not make since
since the postfx shader runs with a window-sized off-screen target as an
input, not the internal render texture.

src/util/postprocessing_shader.h

@@ -49,7 +49,8 @@ public:
   virtual bool CompilePipeline(GPUTexture::Format format, u32 width, u32 height, ProgressCallback* progress) = 0;
 
   virtual bool Apply(GPUTexture* input, GPUTexture* final_target, s32 final_left, s32 final_top, s32 final_width,
-                     s32 final_height, s32 orig_width, s32 orig_height, u32 target_width, u32 target_height) = 0;
+                     s32 final_height, s32 orig_width, s32 orig_height, s32 native_width, s32 native_height,
+                     u32 target_width, u32 target_height) = 0;
 
 protected:
   static void ParseKeyValue(std::string_view line, std::string_view* key, std::string_view* value);