sem/builtins: fix json_populate_record in an edge case

This commit fixes `json_populate_record` builtin in an edge case. In
particular, this generator builtin calls `eval.PopulateRecordWithJSON`
which modifies the passed-in tuple in-place, and right now the builtin
passes the input tuple. This leads to modification of the Datum which is
not allowed. However, this is mostly philosophical bug that doesn't lead
to any actual issues since from a single input tuple the builtin only
generates a single output tuple. I noticed this problem when tried to
re-execute the distributed query as local, but the tuple was corrupted
for that second local execution.

Release note: None

pkg/sql/sem/builtins/generator_builtins.go

@@ -1760,10 +1760,12 @@ func (j *jsonPopulateRecordGenerator) Next(ctx context.Context) (bool, error) {
 
 // Values is part of the tree.ValueGenerator interface.
 func (j jsonPopulateRecordGenerator) Values() (tree.Datums, error) {
-	if err := eval.PopulateRecordWithJSON(j.ctx, j.evalCtx, j.target, j.input.ResolvedType(), j.input); err != nil {
+	output := tree.NewDTupleWithLen(j.input.ResolvedType(), j.input.D.Len())
+	copy(output.D, j.input.D)
+	if err := eval.PopulateRecordWithJSON(j.ctx, j.evalCtx, j.target, j.input.ResolvedType(), output); err != nil {
 		return nil, err
 	}
-	return j.input.D, nil
+	return output.D, nil
 }
 
 func makeJSONPopulateRecordSetGenerator(