Add Image rendering support for ImGui

- Fix alpha channel bug being set to 0

CopiumEngine/src/copium/core/Application.h

@@ -25,6 +25,7 @@ namespace Copium
     std::unique_ptr<DescriptorPool> descriptorPool;
     std::unique_ptr<DescriptorSet> descriptorSet;
     std::unique_ptr<DescriptorSet> descriptorSetPassthrough;
+    std::unique_ptr<DescriptorSet> descriptorSetImGui;
     std::unique_ptr<Scene> scene;
     std::unique_ptr<Mesh> mesh;
     std::unique_ptr<Mesh> meshPassthrough;