Update accesskit to 0.24.0 (and related deps) (#7850)

this patch updates our deps to [accesskit
0.24.0](https://docs.rs/accesskit/0.24.0/accesskit/) (was
[0.21.1](https://docs.rs/accesskit/0.21.1/accesskit/)),
[accesskit_consumer
0.35.0](https://docs.rs/accesskit_consumer/0.35.0/accesskit_consumer/)
(was
[0.30.1](https://docs.rs/accesskit_consumer/0.30.1/accesskit_consumer/)),
and [accesskit_winit
0.32.0](https://docs.rs/accesskit_winit/0.32.0/accesskit_winit/) (was
[0.29.1](https://docs.rs/accesskit_winit/0.29.1/accesskit_winit/)),
allowing egui to be used in apps that use accessibility subtrees
(AccessKit/accesskit#655).

for now, we handle the subtree-related breaking changes by assuming that
egui will use [the root
tree](https://docs.rs/accesskit/0.24.0/accesskit/struct.TreeId.html#associatedconstant.ROOT),
which is good enough for [servoshell](https://github.com/servo/servo)
and does not require any API changes.


* [x] I have followed the instructions in the PR template

<img width="1185" height="954" alt="image"
src="https://github.com/user-attachments/assets/6acfb85a-096d-4a7b-963b-d8549bfc749f"
/>

---------

Co-authored-by: Luke Warlow <lwarlow@igalia.com>
Co-authored-by: lucasmerlin <hi@lucasmerlin.me>
Co-authored-by: Arnold Loubriat <datatriny@gmail.com>

crates/egui-winit/src/lib.rs

@@ -102,7 +102,7 @@ pub struct State {
     has_sent_ime_enabled: bool,
 
     #[cfg(feature = "accesskit")]
-    accesskit: Option<accesskit_winit::Adapter>,
+    pub accesskit: Option<accesskit_winit::Adapter>,
 
     allow_ime: bool,
     ime_rect_px: Option<egui::Rect>,