DragValue loses adjustability when placed inside a rect/child_ui

Nobody has claimed this yet.

I'm building a custom widget and want to include a DragValue inside. When I place it after my widget it works, but when I place it in a child_ui inside my widget it can't be dragged/text entered, only the hover-effect seems to be fine. I have a red triangle (a set point) that can be dragged and adjusted, but I want the position to be also adjustable by a `DragValue`.

Code structure:
```
pub fn gauge_ui(...) -> egui::Response {

let desired_size = egui::vec2(size as f32, size as f32);
let (rect, mut response) = ui.allocate_exact_size(desired_size, egui::Sense::click_and_drag());
if ui.is_rect_visible(rect) {
let visuals = ui.style().interact(&response);
let rect = rect.expand(visuals.expansion);

// draw the cool shapes

if response.dragged() {
let pos = response.interact_pointer_pos();
match pos {
None => {}
Some(p) => {
// update position of triangle
}
}
response.mark_changed(); // report back that the value changed
}
let mut c_ui = ui.child_ui(rect,Layout::default());
c_ui.add(egui::DragValue::new(set)
.min_decimals(1)
.max_decimals(1)
.suffix(suffix));
ui.add(egui::DragValue::new(set)
.min_decimals(1)
.max_decimals(1)
.suffix(suffix));
}
response
}
```
When called by `c_ui` the DragValue will be inside the widget and not controllable, when called by `ui` it will be placed after my widget. What can be done to make the DragValue adjustable inside the other rect?
I'm fairly new to egui, but I really like it so far! Big kudos to everyone involved!

Start with the gauge_ui snippet and reproduce the difference between adding DragValue through c_ui and directly through ui. Read the egui child_ui and DragValue interaction behavior, especially how input regions overlap. Done means the DragValue inside the child rect accepts both dragging and text entry without breaking the surrounding widget.

Written by the indexing model from the issue text.