Loom: Define test groups for development/porting use

It would be beneficial to bring over the Loom-specific test groups from the loom repo to aid development/porting work.

https://github.com/openjdk/loom/blob/fibers/test/jdk/TEST.groups#L97-L108
https://github.com/openjdk/loom/blob/6f42923b3342e41d95b262733205283068802b40/test/hotspot/jtreg/TEST.groups#L111-L125