[Feature] Support IME “Send” action for message submission

[PRO-2684]

Description:

Some input methods (IMEs) replace the “Enter” key with a “Send” action in messaging contexts.

Expected behavior:

• When the IME shows a “Send” button, pressing it should send the message instead of inserting a newline.

Fallback for newline:

• Paste a line break, or
• Use IME-specific alternatives (e.g., long-press the key, if supported)

Rationale:

• Matches common messaging app behavior
• Improves input efficiency on mobile devices

Reference screenshots:

IME showing “Send” instead of “Enter”

Long-press to insert newline