On macOS, the builtin 2-Set Korean IME's hanja candidate window cannot be opened with `Option+Return`

**Describe the bug**

On macOS, while using the builtin 2-Set Korean IME, the user normally can open the hanja candidate window with Option+Return.
The section “Convert Hangul to Hanja” of [this User Guide by Apple](https://support.apple.com/en-am/guide/korean-input-method/welcome/mac) illustrates this.

On 0.33.3 and [current main], this key combination does not work.

It doesn't seem that Apple provides an option to change the keybinding for it, so I can't tell whether this bug is related to this specific key combination or not.

**To Reproduce**
Steps to reproduce the behavior:
1. run the demo App.
2. open the TextEdit demo.
3. Switch to the builtin 2-Set Korean IME and type `gks` in the TextEdit. (You may need to type something else first with the Korean IME due to [this winit bug](https://github.com/rust-windowing/winit/issues/3095))
4. hit Option+Return.
5. Instead of the hanja candidate window being opened, a new line is entered.

**Expected behavior**
The hanja candidate window should be opened at the 5th step of the reproduction above.

**Screenshots**

Working example on macOS (within TextEdit.app)


Broken behavior in egui on macOS


On Windows, the builtin Korean IME uses the Ctrl key for the same thing, and it works


On Linux, the Korean Hangul IME for both IBus and Fcitx5 supports using customizable keybindings (with F9 being one of the default) to open the hanja candidate window, and that works in egui just like Windows.
(I could open the hanja candidate window with Ctrl yesterday, but I can't do that anymore for no reason. This is unlikely related to egui, since every program is affected.)

**Desktop (please complete the following information):**
- OS: macOS 15.7.3
- Native (eframe)
- Version 0.33.3 and [current main]

[current main]: https://github.com/emilk/egui/commit/14afefa2521d1baaf4fd02105eec2d3727a7ac36

Start by running the demo App, opening the TextEdit demo, and reproducing the issue with macOS's builtin 2-Set Korean IME and Option+Return. Trace the macOS keyboard and text-input handling involved in the TextEdit demo. Done means Option+Return opens the hanja candidate window instead of inserting a new line, while the existing Windows and Linux behavior remains intact.

Written by the indexing model from the issue text.