The Tree/Explorer should not prevent dragging representations

[pcdavid]

In TreeItem we do:

sirius-web/packages/trees/frontend/sirius-components-trees/src/treeitems/TreeItem.tsx

Lines 374 to 377 in 2e8ab3b

	const draggable = kind.startsWith('siriusComponents://semantic') && item.selectable;
	const dragStart: React.DragEventHandler<HTMLDivElement> = (event) => {
	const entries = selection.entries.filter((entry) => entry.kind.startsWith('siriusComponents://semantic'));

which prevents dragging any tree item which represents something else than a semantic element.
In particular, this prevents dragging representations, which is something we want for e.g. #2765.

The tree representation should no try and impose any restriction on what can be dragged. It's up to each drop target to decide if it supports a particular kind of item.