Add an interaction group to specify fluid/boundary interactions

[ThierryBerger]

• Fix Filtering liquids with rapier rigidbodies based on masks/layers #57

TODO:

• This PR doesn´t add the capacity to add interaction group between fluids (yet? It seems to be possible but didn´t look much into it yet.)
• check benchmarks

[sebcrozet]

Looks good, thank you!

[sebcrozet]

There is a good chance that adding support for groups between two fluids is only a matter of adding a check in this branch too.

[Ughuuu]

So this adds just between fluid/boundary? Still, thanks for this PR.

[ThierryBerger]

So this adds just between fluid/boundary? Still, thanks for this PR.

Yes ; fluid / fluid layers will be studied in a follow up PR 🤞