Is what occurs by way of ejaculation when lying on the stomach in a state between sleep and wakefulness considered masturbation, and does it invalidate the Ramadan daytime fast and necessitate making it up?

If semen is discharged without any action from the fasting person and they were unable to control themselves in that state, this is considered a wet dream (احتلام). A wet dream does not invalidate the fast, by scholarly consensus.