SvelteFlow on:selectionchange doesn't get called

[Sahasrara]

Describe the Bug

I just noticed that on:selectionchange is never called in SvelteFlow.

Your Example Website or App

No response

Steps to Reproduce the Bug or Issue

Try assigning a handler to on:selectionchange

<SvelteFlow
    on:selectionchange={onSelectionChanged}
/>

The onSelectionChanged function is never called.

Expected behavior

I would expect onSelectionChanged to be called when:

1. A node or edge is clicked that wasn't already selected
2. A selection rectangle is drawn

Screenshots or Videos

No response

Platform

• OS: Windows
• Browser: Electron
• Version: ^28.1.1

Additional context

No response

[moklick]

That handler doesn't exist. Where did you find it?

[Sahasrara]

Oh! I figured it existed based on my conversation with Peter here:
https://discord.com/channels/771389069270712320/1118204997671334019/1209083389286547467

But if that event doesn't exist, then I assume we're supposed to rely on on:nodedragstop, but I don't see that being called when you're dragging a selection.

[peterkogo]

@Sahasrara You can track the progress on this here. If this pull request lands, you will receive nodedragstop events, when you drag the selection box, too.