Assistant: Make Provider ref-counted

Author: https://github.com/Rummskartoffel
Commit: ada1d4906e
Pull-request: https://github.com/SerenityOS/serenity/pull/11919
Issue: https://github.com/SerenityOS/serenity/issues/11766
Reviewed-by: https://github.com/alimpfard ✅
Reviewed-by: https://github.com/awesomekling

Userland/Applications/Assistant/Providers.h

@@ -128,7 +128,7 @@ private:
     RefPtr<Gfx::Bitmap> m_bitmap;
 };
 
-class Provider {
+class Provider : public RefCounted<Provider> {
 public:
     virtual ~Provider() = default;