🉐 fix: incorrect handling for composing CJK texts in Safari

[oonishi3]

Summary

Fixed an issue where line breaks were not correctly applied in Mac/Safari environments for languages that require pressing the Enter key to confirm text input (e.g., Japanese, Chinese, etc.).

This issue was largely resolved for most environments in #3103, but the problem persisted in Mac/Safari due to differences in the behavior of isComposing.

In addition to using isComposing for composition detection, there are also KeyboardEvent.key and KeyboardEvent.keyCode. However, in Mac/Safari, it was impossible to make correct judgments using either isComposing or KeyboardEvent.key, so I reluctantly used keyCode for detection, despite it being deprecated.

To prevent issues when keyCode is removed in the future, I have implemented the keyCode-based detection after attempting detection using isComposing and key.

This PR appears to be related to #3412.

Change Type

• Bug fix (non-breaking change which fixes an issue)

Testing

Testing can be done using a similar approach as in #3103.

When creating the pull request, I conducted tests in the following environment:

OS	Browser	note
macOS 15.2	Safari 18.2 (20620.1.16.11.8)
macOS 15.2	Chrome 131.0.6778.267
Windows 11 (23H2)	Chrome 132.0.6834.111
Windows 11 (23H2)	Firefox 134.0.2
Android 15	Chrome 132.0.6834.122
iPadOS 16.5	Safari	Due to the limitations of the device I own, I'm using a slightly older version.

Checklist

Please delete any irrelevant options.

• My code adheres to this project's style guidelines
• I have performed a self-review of my own code
• I have commented in any complex areas of my code
• My changes do not introduce new warnings
  • ⚠️ While no warnings appear during testing or building, many IDEs display strikethrough lines on the relevant parts due to the use of deprecated properties.