support specifying JDK version and download appropriate OpenJDK version

[propensive]

Adopt OpenJDK provides an API for selecting and downloading OpenJDK releases.

[odisseus]

Specifying a required JDK is a good idea, but downloading it automatically probably isn't.

I think the users should have the freedom to provide their preferred distributions of the JDK (OpenJDK, Oracle, IBM, or even customized ones), and maybe even override the project requirements (e. g. attempting to compile Scala code with JDK 11).

[propensive]

I think it's acceptable for a) the projects which demand an exact JDK version (most of them won't), and b) as long as we don't install the JDK on their system, and just use it internally to Fury.