Bug#35658656 Memory leaks hidden by global heap

The HW global heap no longer garbage collects leaking allocations;
these allocations must be properly handled from now on.

Changes:
- Call the destructor on the non-trivial classes RapidColumn and
  HtEntry before freeing memory.
- Fix the setters of ConfigurationValueExternalJSON to delete the old
  values.
- Add RTLD_NODELETE to dlopen in sql_plugin.cc when building with
  HAVE_ASAN or HAVE_LSAN.
- In ctests, reset the configuration before deleting the Heap.
- Configuration::getObjStoreParam returns a rapid::util::UniquePtr.

Change-Id: I8e4ddff653a2f226d17ea6f37d0c31d647da0352

Author: Georgios Psaropoulos

sql/sql_plugin.cc

@@ -687,7 +687,15 @@ static st_plugin_dl *plugin_dl_add(const LEX_STRING *dl, int report,
   plugin_dl.ref_count = 1;
   /* Open new dll handle */
   mysql_mutex_assert_owner(&LOCK_plugin);
-  if (!(plugin_dl.handle = dlopen(dlpath, RTLD_NOW))) {
+#if defined(HAVE_ASAN) || defined(HAVE_LSAN)
+  // Do not unload the shared object during dlclose().
+  // LeakSanitizer needs this in order to match entries in lsan.supp
+  plugin_dl.handle = dlopen(dlpath, RTLD_NOW | RTLD_NODELETE);
+#else
+  plugin_dl.handle = dlopen(dlpath, RTLD_NOW);
+#endif
+
+  if (plugin_dl.handle == nullptr) {
     const char *errmsg;
     const int error_number = dlopen_errno;
     /*