RedoLogReader: Sweeps through the redo logs and parse log records

For every log record a method in the handler will be invoked. This code can be used as a diagnosing tool. E.g., we can use this to find which tablespaces are changed in most recent transactions. We can implement custom handlers find other information we need.

Not intended to push back to Maria but anyone interested can make use of this tool.

Pull request: https://github.com/MariaDB/server/pull/2195