Query explanation not showing HAVING node

[hmottestad]

Discussed in https://github.com/eclipse-rdf4j/rdf4j/discussions/5129

SPARQL query with a HAVING node will show an incorrect query explanation because the HAVING node is not part of the query explanation. This makes it seem like the query is returning more results than expected.

Plan:

• Make tests in QueryPlanRetrievalTest
• Understand how the ASTHavingClause is represented using TupleExpr by taking a look at the private TupleExpr processHavingClause(ASTHavingClause havingNode, TupleExpr tupleExpr, Group group) method in TupleExprBuilder