feat(library/init/meta/relation_tactics): add tactic for retrieving lhs and rhs from an registered relation
feat(library/init/meta/relation_tactics): add tactic for retrieving lhs and rhs from an registered relation

dselsam/lean,avigad/lean,rlewis1988/lean,dselsam/lean,avigad/lean,rlewis1988/lean,leanprover-community/lean,fpvandoorn/lean,dselsam/lean,leanprover/lean,avigad/lean,Kha/lean,Kha/lean,avigad/lean,fgdorais/lean,digama0/lean,rlewis1988/lean,Kha/lean,fgdorais/lean,leanprover-community/lean,johoelzl/lean,leanprover/lean,fgdorais/lean,leodemoura/lean,digama0/lean,johoelzl/lean,digama0/lean,rlewis1988/lean,leanprover/lean,leodemoura/lean,leodemoura/lean,fgdorais/lean,leanprover/lean,dselsam/lean,johoelzl/lean,fpvandoorn/lean,digama0/lean,fgdorais/lean,johoelzl/lean,digama0/lean,dselsam/lean,Kha/lean,fpvandoorn/lean,avigad/lean,rlewis1988/lean,leanprover-community/lean,leanprover-community/lean,fpvandoorn/lean,digama0/lean,leodemoura/lean,rlewis1988/lean,leodemoura/lean,fpvandoorn/lean,fgdorais/lean,leodemoura/lean,leanprover-community/lean,Kha/lean,leanprover-community/lean,fpvandoorn/lean,leanprover/lean,leanprover/lean,Kha/lean,johoelzl/lean,johoelzl/lean,dselsam/lean,avigad/lean