Fix IME preedit overlay and add tests

[Tryanks]

before

after

[JRBros2346]

Run cargo fmt and push changes. It must make the Checks to pass

[u1-liquid]

The current CI failure appears to be caused by an external factor rather than this change.
If this fix is merged, it will significantly improve usability for CJK users, so it would be very helpful if the priority could be raised.

At the moment, the IME pre-edit text is not rendered at all, and users sometimes have to rely on a popup that is completely misaligned to input text. This makes typing quite inconvenient for CJK users.

[JRBros2346]

The current CI failure appears to be caused by an external factor rather than this change.

Yup. For some reason, the windows CI often gets stuck and gets auto cancelled after 6h. All the other CI's are passed tho.