Node expansion via drag event misses to async load tree data

Status Quo

The tree component is expanding the tree node, if the user has dragged over the tree node for longer time.
Thus, the tree comonent is expanding this particular tree node, hence tree is showing the children of that tree node, as well.

Problem

The tree component does not ensure that the tree data is fetched, if lazy load is used, once the tree node is expanded via drag enter/over event.

Root cause

It seems only the expanded keys are updated and onExpand is getting called, see:
https://github.com/react-component/tree/blob/22c5ace87f7c27a452b444a63e1a927488525520/src/Tree.tsx#L565

Solution Proposal

The onNodeExpand function should be called in case of expansion via drag event, like it is done for keyboard navigation or mouse-click event, since this ensures the async load.

Start in src/Tree.tsx around line 565, then compare the drag expansion path with the keyboard-navigation and mouse-click paths that call onNodeExpand. Confirm that expanding a node through drag events also fetches lazy-loaded children; done means the async tree data loads after drag expansion, matching the other expansion interactions.