Improve support for declarative partitioning.

Generated SQL for a partition is now correct (atleast for simple cases)
Switched to C++ 20 so the ranges library can be used in this case
to filter unwanted items.

pglablib/catalog/PgConstraint.h

@@ -79,6 +79,10 @@ public:
 
 	QString dropSql() const override;
 	QString createSql() const override;
+    bool isInherited() const
+    {
+        return inhcount > 0;
+    }
 };