Support BindParams in subqueries

When an Arel AST contains a SelectManager as a component, e.g. as a CTE
expression, the SelectManager is converted to SQL with `#to_sql`. This
uses a new collector that leads to invalid expressions when using
bind parameters. For example, when generating PostgreSQL queries, the
bind parameter number starts from one again. When using the
SubstituteBinds collector, binds in the subquery are not substituted.

This commit changes the ToSql visitor to visit the SelectManager ast
itself.

Author: jgraichen

lib/arel/visitors/to_sql.rb

@@ -427,7 +427,8 @@ def visit_Arel_Nodes_Grouping o, collector
       end
 
       def visit_Arel_SelectManager o, collector
-        collector << "(#{o.to_sql.rstrip})"
+        collector << '('
+        visit(o.ast, collector) << ')'
       end
 
       def visit_Arel_Nodes_Ascending o, collector