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_fx.h

@@ -31,7 +31,8 @@ public:
   bool ResizeOutput(GPUTexture::Format format, u32 width, u32 height) override;
   bool CompilePipeline(GPUTexture::Format format, u32 width, u32 height, ProgressCallback* progress) override;
   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) override;
+             s32 final_height, s32 orig_width, s32 orig_height, s32 native_width, s32 native_height, u32 target_width,
+             u32 target_height) override;
 
 private:
   using TextureID = s32;
@@ -60,6 +61,11 @@ private:
     InternalHeight,
     InternalWidthF,
     InternalHeightF,
+    NativeWidth,
+    NativeHeight,
+    NativeWidthF,
+    NativeHeightF,
+    UpscaleMultiplier,
 
     MaxCount
   };