[Improvements Request] MudTransferList with <empty> items/message + better 3 flex columns handling

[thepra]

As of right now there's no way to set empty list messages(so they don't appear like empty horizontal containers, and the generated html could be better because the 3 horizontal columns(first and last being naked <div>s don't stretch to available space, it would be better to fill those <div>s with classes d-flex flex-col flex-1 when being horizontal only.

[mckaragoz]

Sorry i don't understand. What do you want exactly when a list has no items, to have same height or show nothing?

[thepra]

Have a settable child component like <EmptyListContent></EmptyListContent> where I can show some message of empty collection or any other container that replaces the main one, like a same-height container with the "empty" message inside.

[mckaragoz]

We have some fix with #549 . But for the NoItemContent we should add it MudListExtended first. So opened #550 , we can continue to there.