Drag and drop list in Blazor

Minimal implementation of drag & drop list. Blazor WebAssembly.

No extra js library needed.

Whole implementation is in Index.razor.

More advanced solution with child elements: Index2.razor (resolves this SO issue 'dragleave' of parent element fires when dragging over children elements )

Inspirated by: https://chrissainty.com/investigating-drag-and-drop-with-blazor/