egui: Change Ui::allocate_painter to inherit properties from Ui (…

…#4343)

The painter, allocated by `Ui::allocate_painter`, doesn't inherit
properties from the `Ui` object, leading to improper widget rendering in
`egui`.

Specifically, if the `Ui` object is disabled, the corresponding painter
should also be disabled.

crates/egui/src/ui.rs

@@ -1001,7 +1001,7 @@ impl Ui {
     pub fn allocate_painter(&mut self, desired_size: Vec2, sense: Sense) -> (Response, Painter) {
         let response = self.allocate_response(desired_size, sense);
         let clip_rect = self.clip_rect().intersect(response.rect); // Make sure we don't paint out of bounds
-        let painter = Painter::new(self.ctx().clone(), self.layer_id(), clip_rect);
+        let painter = self.painter().with_clip_rect(clip_rect);
         (response, painter)
     }