XIM servers currently do not support preedit area reporting from
clients and there may be no standard way to report it.
Fcitx and iBus both place the candidate window descending descending
from the caret, with the reported X font; but since winit does not
report a font, the height of the line is assumed 0, so when we report
the top left corner of the cursor area they will tend to obscure it.
Taking this into account, the best default option is to report the
bottom right corner of the cursor area, because it will tend not to
obscure the preedit area when using `Window::set_ime_cursor_area` in
the way suggested by documentation.
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