This fixes the behavior in notepad, with Japanese ibus-mozc IME, when typing "NIHONGO-SPACE-NO", or with Korean ibus-hangul when typing "GA-NA-DA". The latter still has an issue with the last character not appearing in the a composition but I believe it is unrelated to comctl32 and will be fixed by some future imm32 changes.
-- v3: user32: Keep and display composition separate from the selection. comctl32/edit: Keep and display composition separate from the selection.