WIP: Add JRuby support to use in rb-sys tests

[uvlad7]

I added JRuby variant of the implementation to use it here.
It's WIP and won't pass the pipeline:

• rb_sys requirements in Gemfile and gemspec need to be updated after new version of rb-sys gem is released.
• oxidize-rb/actions/setup-ruby-and-rust@v1 doesn't work, see
• It doesn't build on Windows and it seems I need help with it.

I also want to add jruby build into the cross-gem action, but it's not required for rb-sys, so it has low priority.