Enhance: DevUI has bad UX when inputting Japanese (Re-open #6)

[Description of issue]
On DevUI chat input, we can send a message by typing the Enter Key.
When inputting Japanese, we must decide the conversion candidate by pressing the Enter key, but DevUI chat input send the message when decide the conversion candidate.
So we can't send full message when using Japanese.

[How to re-produce the issue]

Show DevUI
Input Japanese message on chat input.
[Proposal]
Changing the shortcut key to Ctrl(Command) + Enter or adding the send button and disable shortcut key.
Or using isComposing property.
https://developer.mozilla.org/en-US/docs/Web/API/KeyboardEvent/isComposing

Note: #6 was closed, but #6 have not fixed yet. I don't have the permission to re-open the issue, so i create new issue now.