add openjdk emscripten port

[wangyenshu]

https://github.com/bmarti44/javabox This repo compiles (part of) the openjdk 21 by emscripten. That is quite interesting. If a complete openjdk is compiled, then java software can run in browser without touching the binary.

[DerThorsten]

That would indeed be nice.
Recipes are welcome