Underline text if in dead key state (#7488)

This highlights dead keys. Example: when in Brazilian keyboard layout
and typing `"` it's now underlined.



https://github.com/zed-industries/zed/assets/1185253/a6b65f7b-1007-473d-ab0f-5d658faa191b



Release Notes:

- Fixed dead keys not being underlined.

Co-authored-by: Antonio <antonio@zed.dev>