[Windows] IME popovers are displayed at the wrong position

[angelosilvestre]

On Windows desktop, the IME panels like the emoji picker (windows + .) are displayed in the wrong position:

2023-09-20.22-21-32.mp4

The reason is that, on Windows desktop, Flutter doesn't implement the setCaretRect method, which is needed to position the panels at the correct position.

Related Flutter issue: flutter/flutter#74547