[memory] refactor storageprovider factory method

since it's common in downstream modules to have a
type alias for the full storageprovider template
I've added a static method that can be called
from that type w/o needing to extract the
stored type again

dune/xt/common/memory.hh

@@ -339,6 +339,12 @@ public:
     return storage_->access();
   }
 
+  template <typename... Args>
+  static ConstStorageProvider<T> make(Args&&... args)
+  {
+    return ConstStorageProvider<T>(new T(std::forward<Args>(args)...));
+  }
+
 private:
   std::unique_ptr<const internal::ConstAccessInterface<T>> storage_;
 }; // class ConstStorageProvider
@@ -347,7 +353,7 @@ private:
 template <typename T, typename... Args>
 ConstStorageProvider<T> make_const_storage(Args&&... args)
 {
-  return ConstStorageProvider<T>(new T(std::forward<Args>(args)...));
+  return ConstStorageProvider<T>::make(std::forward<Args>(args)...);
 }
 
 
@@ -409,6 +415,12 @@ public:
     return storage_->access();
   }
 
+  template <typename... Args>
+  static StorageProvider<T> make(Args&&... args)
+  {
+    return StorageProvider<T>(new T(std::forward<Args>(args)...));
+  }
+
 private:
   std::unique_ptr<internal::AccessInterface<T>> storage_;
 }; // class StorageProvider
@@ -417,10 +429,9 @@ private:
 template <typename T, typename... Args>
 StorageProvider<T> make_storage(Args&&... args)
 {
-  return StorageProvider<T>(new T(std::forward<Args>(args)...));
+  return StorageProvider<T>::make(std::forward<Args>(args)...);
 }
 
-
 //! dumps kernel stats into a file
 void mem_usage(std::string filename);