Fix move semantics misuse and unhide Equals() overload

- In pax_storage, remove unnecessary std::move when returning a
  std::unique_ptr from GetGroupStatsInfo(). Returning directly avoids
  warnings and redundant moves.
- In gporca/gpos, bring CWStringBase::Equals(const WCHAR*) into scope
  in CWStringConst to prevent it from being hidden by the derived class
  overload.

Author: yjhjstz

contrib/pax_storage/src/cpp/storage/micro_partition.cc

@@ -91,7 +91,7 @@ size_t MicroPartitionReaderProxy::GetTupleCountsInGroup(size_t group_index) {
 
 std::unique_ptr<ColumnStatsProvider>
 MicroPartitionReaderProxy::GetGroupStatsInfo(size_t group_index) {
-  return std::move(reader_->GetGroupStatsInfo(group_index));
+  return reader_->GetGroupStatsInfo(group_index);
 }
 
 std::unique_ptr<MicroPartitionReader::Group>

src/backend/gporca/libgpos/include/gpos/string/CWStringConst.h

@@ -57,6 +57,9 @@ class CWStringConst : public CWStringBase
 
 	// checks whether the string is byte-wise equal to another string
 	BOOL Equals(const CWStringBase *str) const override;
+
+	// bring base class Equals(const WCHAR*) into scope to avoid hiding
+	using CWStringBase::Equals;
 };
 }  // namespace gpos