InnoDB recovery is duplicating log records

Starting with MDEV-14425, InnoDB log records are being written contiguously. Only when the server has been configured with innodb_encrypt_log=ON or a log record is wrapping from the end of a log file, is it necessary to actually copy log records.

Especially with the settings innodb_log_file_mmap=ON and innodb_encrypt_log=OFF we could make recv_sys.pages point straight to entire mini-transaction logs. Yes, a mini-transaction may modify several pages, but we could simply filter out the records that refer to other pages than the one we are currently applying changes to.

If we are recovering with innodb_log_file_mmap=OFF or innodb_encrypt_log=ON, we could read the log into a large contiguous buffer that is allocated right from the buffer pool, and similarly make recv_sys.pages point to this buffer.