Deprecated ImageButton and removed WidgetType::ImageButton (#7483)

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* Closes <https://github.com/emilk/egui/issues/7466>
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Added the deprecated tag to ImageButton struct
Removed the `WidgetType::ImageButton` variant. ImageButton will use
`WidgetType::Button` for its WidgetInfo

*This is my first PR ever, please let me know if I did something wrong
so I can change it*

---------

Co-authored-by: Nicolas <bircni@icloud.com>
Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>
Co-authored-by: Lucas Meurer <hi@lucasmerlin.me>

crates/egui/src/widgets/mod.rs

@@ -24,6 +24,7 @@ pub mod text_edit;
 
 #[expect(deprecated)]
 pub use self::selected_label::SelectableLabel;
+#[expect(deprecated, reason = "Deprecated in egui 0.33.0")]
 pub use self::{
     button::Button,
     checkbox::Checkbox,