TextArea cannot delete multi-symbol emoji using backspace at once, such as 👨‍👨‍👧‍👧

For TextArea, if you use backspace once, you cannot completely delete the multi-symbol unicode emoji, such as 👨‍👨‍👧‍👧.
I noticed that the implementation of `QTextCursor::deletePreviousChar()` is the same as
Unlike `QTextCursor::deleteChar()`, `deletePreviousChar()` only considers a single proxy pair, and does not involve the scenario of using 0x200D to connect multiple proxy pairs.