Handle the IME event first in TextEdit to fix some bugs (#4794)

Handle the `IME` event first 
There is a need to handle the Ime event first.

Fix Issues : When you press `BackSpace`, the entire text is erased, and
when you press another letter, it appears again.
Fix Issues : When you press `Left`, the character being entered will be
copied once more.
Fix Issues : When you press `Enter`, `Enter` with `repeat` set is
entered and `Enter` is entered twice.
Fix Issues : When you press a key in `IME` mode, `repeat` is often set.

Fix Issues : Since you may be selecting something in the IME, this also
disables the `Arrow` keys.

crates/egui/src/widgets/text_edit/builder.rs

@@ -855,7 +855,14 @@ fn events(
 
     let mut any_change = false;
 
-    let events = ui.input(|i| i.filtered_events(&event_filter));
+    let mut events = ui.input(|i| i.filtered_events(&event_filter));
+
+    if state.ime_enabled {
+        remove_ime_incompatible_events(&mut events);
+        // Process IME events first:
+        events.sort_by_key(|e| !matches!(e, Event::Ime(_)));
+    }
+
     for event in &events {
         let did_mutate_text = match event {
             // First handle events that only changes the selection cursor, not the text:
@@ -1055,6 +1062,27 @@ fn events(
 
 // ----------------------------------------------------------------------------
 
+fn remove_ime_incompatible_events(events: &mut Vec<Event>) {
+    // Remove key events which cause problems while 'IME' is being used.
+    // See https://github.com/emilk/egui/pull/4509
+    events.retain(|event| {
+        !matches!(
+            event,
+            Event::Key { repeat: true, .. }
+                | Event::Key {
+                    key: Key::Backspace
+                        | Key::ArrowUp
+                        | Key::ArrowDown
+                        | Key::ArrowLeft
+                        | Key::ArrowRight,
+                    ..
+                }
+        )
+    });
+}
+
+// ----------------------------------------------------------------------------
+
 /// Returns `Some(new_cursor)` if we did mutate `text`.
 fn check_for_mutating_key_press(
     os: OperatingSystem,