Fix tooltips being dragged along in graph view (#8573)

### Related

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Include links to any related issues/PRs in a bulleted list, for example:
* Closes #1234
* Part of #1337
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* Closes #8568.

### What

This fixes the problem by tying to tooltip position to the node position
instead of the the pointer, with the nice side-effect that tooltips can
now be interacted with in the graph view.

There is some weirdness with tooltips opening for the tooltips, but we
should probably tackle that separately.

<img width="607" alt="image"
src="https://github.com/user-attachments/assets/43e0edba-49b6-4f49-a279-0982320c4ef6"
/>

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Author: grtlr

crates/viewer/re_view_graph/src/ui/draw.rs

@@ -349,7 +349,7 @@ pub fn draw_graph(
                 let instance_path =
                     InstancePath::instance(entity_path.clone(), instance.instance_index);
 
-                response = response.on_hover_ui_at_pointer(|ui| {
+                response = response.on_hover_ui(|ui| {
                     list_item::list_item_scope(ui, "graph_node_hover", |ui| {
                         item_ui::instance_path_button(
                             ctx,