fix(memory leaks): MCOL-5791 - get rid of memory leaks in plugin code (#3365)

There were numerous memory leaks in plugin's code and associated code.
During typical run of MTR tests it leaked around 65 megabytes of
objects. As a result they may severely affect long-lived connections.

This patch fixes (almost) all leaks found in the plugin. The exceptions
are two leaks associated with SHOW CREATE TABLE columnstore_table and
getting information of columns of columnstore-handled table. These
should be fixed on the server side and work is on the way.

writeengine/shared/we_brm.h

@@ -23,6 +23,7 @@
 
 #pragma once
 
+#include <atomic>
 #include <iostream>
 #include <memory>
 #include <vector>
@@ -474,6 +475,8 @@ class BRMWrapper : public WEObj
   static IDBDataFile* m_curVBFile;
 
   BRM::DBRM* blockRsltnMgrPtr;
+
+  EXPORT static std::atomic<bool> finishReported;
 };
 
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