ORCA: Fix memory leak in CWindowOids by adding destructor

CWindowOids class was leaking three CMDIdGPDB objects (m_MDIdRowNumber,
m_MDIdRank, m_MDDenseRank) that were allocated in the constructor but
never released.

Fixes ORCA unit test failures:
  - gporca_test_CXformTest
  - gporca_test_CConstExprEvaluatorDefaultTest

Author: yjhjstz

src/backend/gporca/libgpopt/include/gpopt/base/CWindowOids.h

@@ -60,6 +60,8 @@ class CWindowOids : public CRefCount
 	CWindowOids(CMemoryPool *mp, OID row_number_oid, OID rank_oid,
 				OID dense_rank_oid);
 
+	~CWindowOids() override;
+
 	// accessor of oid value of "row_number" function
 	OID OidRowNumber() const;
 	IMDId *MDIdRowNumber() const;

src/backend/gporca/libgpopt/src/base/CWindowOids.cpp

@@ -18,6 +18,13 @@ CWindowOids::CWindowOids(CMemoryPool *mp, OID row_number_oid, OID rank_oid,
 	m_MDDenseRank = GPOS_NEW(mp) CMDIdGPDB(IMDId::EmdidGeneral, m_oidDenseRank);
 }
 
+CWindowOids::~CWindowOids()
+{
+	m_MDIdRowNumber->Release();
+	m_MDIdRank->Release();
+	m_MDDenseRank->Release();
+}
+
 OID
 CWindowOids::OidRowNumber() const
 {