hg: openjfx/2.1/master: Added build scripts that are needed for building UI controls.

[Roman Kennke]

> I think modifying the build scripts so that they also produce maven-compatible artifacts is fine, I know this has been asked for frequently. We don't know how to do it though (I don't know any of our team that has any significant time in Maven).

I could take a look at this. Problem is that this would be very
difficult (and a bit pointless) as long as the other pieces are not open
sourced. Those would need to get provided in a publicly accessible Maven
repository to be of any use for building the open source part.

Regards, Roman