Console log error in drag n drop when missing selection feature

[crusaider]

Describe the bug
Browser Console Message
Uncaught Error: Headless Tree: drag-and-drop needs selection

To Reproduce
Create a tree with DnD feature omitting the selection feature

Expected behavior
Did not expect the error since the documentation gives the impression that the selection feature is optional when using DnD. https://headless-tree.lukasbach.com/dnd/overview/

Library versions
"@headless-tree/core": "^1.2.1",
"@headless-tree/react": "^1.2.1",

[lukasbach]

At the moment, the selection feature is required for the drag-and-drop feature, looks like I wrote that incorrectly in the docs. But it might make sense to change the DnD feature to fall back to the focused item if the selection feature is not available, I'll look into that once I have some time.

[lukasbach]

In the latest release, I've removed the dependency of DnD on selections, and made it so that it defaults to the focused item if selections are not used. Thanks again for the report!