Create custom egui_kittest::Node (#7138)

This adds a custom Node struct with proper support for egui types
(`Key`, `Modifiers`, `egui::Event`, `Rect`) instead of needing to use
the kittest / accesskit types.

I also changed the `click` function to do a proper mouse move / mouse
down instead of the accesskit click. Also added `accesskit_click` to
trigger the accesskit event. This resulted in some changed snapshots,
since the elements are now hovered.

Also renamed `press_key` to `key_press` for consistency with
`key_down/key_up`.

Also removed the Deref to the AccessKit Node, to make it clearer when to
expect egui and when to expect accesskit types.

* Closes #5705 
* [x] I have followed the instructions in the PR template

crates/egui_demo_lib/src/demo/text_edit.rs

@@ -113,8 +113,8 @@ impl crate::View for TextEditDemo {
 
 #[cfg(test)]
 mod tests {
-    use egui::{accesskit, CentralPanel};
-    use egui_kittest::kittest::{Key, Queryable as _};
+    use egui::{accesskit, CentralPanel, Key, Modifiers};
+    use egui_kittest::kittest::Queryable as _;
     use egui_kittest::Harness;
 
     #[test]
@@ -133,8 +133,9 @@ mod tests {
 
         let text_edit = harness.get_by_role(accesskit::Role::TextInput);
         assert_eq!(text_edit.value().as_deref(), Some("Hello, world!"));
+        text_edit.focus();
 
-        text_edit.key_combination(&[Key::Command, Key::A]);
+        harness.key_press_modifiers(Modifiers::COMMAND, Key::A);
         text_edit.type_text("Hi ");
 
         harness.run();