"match shapes" node expression

[afs]

From #517 (comment)

        shnex:match [
            sh:class ex:Person ;
            sh:property [
                sh:path ex:age ;
                sh:minInclusive 18 ;
                sh:minCount 1 ;
            ]

A node expression that returns a list of shape resources would make applying rules to shapes within a rule set possible.

[HolgerKnublauch]

Makes sense, now that engines will likely have this algorithm implemented anyway, for sh:targetWhere.