shader: Decode SUST and implement backing image functionality

src/video_core/renderer_vulkan/vk_shader_decompiler.cpp

@@ -935,6 +935,11 @@ private:
         return {};
     }
 
+    Id ImageStore(Operation operation) {
+        UNIMPLEMENTED();
+        return {};
+    }
+
     Id Branch(Operation operation) {
         const auto target = std::get_if<ImmediateNode>(&*operation[0]);
         UNIMPLEMENTED_IF(!target);
@@ -1326,6 +1331,8 @@ private:
         &SPIRVDecompiler::TextureQueryLod,
         &SPIRVDecompiler::TexelFetch,
 
+        &SPIRVDecompiler::ImageStore,
+
         &SPIRVDecompiler::Branch,
         &SPIRVDecompiler::PushFlowStack,
         &SPIRVDecompiler::PopFlowStack,