feat(windows,mac,linux): try to show the result of a deadkey in OSK

If I hit a deadkey, in the OSK, it would be nice if the OSK showed some indication that this was a deadkey, and could shift to "preview" the expected result when I push the next key.
For Example: if I press Deadkey dk(0300), I would like the OSK to show me any configured outputs on the appropriate keys: à, è, ù, etc. This way, I can see (and choose) what to expect, much like mobile. I realize that this could become complex in some languages and may steal some processing power, but it would be a boost to usability.

My deadkeys only have one following character: ;d = ɗ. I don't know how it should be implemented if the deadkey requires several key presses until complete.