PS-9378: Backport PS-9302 (WRITESET perf improvements) to 8.0

https://perconadev.atlassian.net/browse/PS-9378

Cherry-piked PS-9302
"Improve performance for binlog_transaction_dependency_tracking=WRITESET"
(https://perconadev.atlassian.net/browse/PS-9302) from 8.4.

Problem:
Comparing to 8.0 where the default value of
binlog_transaction_dependency_tracking was COMMIT_ORDER, 8.4 introduces
a visible write performance drop.

Cause:
8.4 uses WRITESET dependency tracking. For this tracking we maintain
a map of binlog_transaction_dependency_history_size for row_id to newest
transaction sequence_number which modified a given row. Every new
transaction needs to check its dependency by examining the map (find),
which is done with logarithmic complexity.

Solution:
Change std::map to std::unordered_map. This allows us to find a row
dependency in constant on average complexity.

sql/rpl_trx_tracking.h

@@ -27,7 +27,7 @@
 #include <assert.h>
 #include <sys/types.h>
 #include <atomic>
-#include <map>
+#include <unordered_map>
 
 #include "libbinlogevents/include/binlog_event.h"
 
@@ -157,7 +157,7 @@ class Writeset_trx_dependency_tracker {
     Track the last transaction sequence number that changed each row
     in the database, using row hashes from the writeset as the index.
   */
-  typedef std::map<uint64, int64> Writeset_history;
+  typedef std::unordered_map<uint64, int64> Writeset_history;
   Writeset_history m_writeset_history;
 };