[TASK] Better index on sys_log

Looking at the selects performed on sys_log in the core
of TYPO3 reveals that a combination of tstamp, type, userid
should giver a better performance for at least 2 SQL
statements. One performing a full-table scan - the other
approximately half a full-table scan.

On installations where a few users have created a lot of entries
in sys_log the existing indexes event and user_auth will return
too many rows compared to the new combined index.

Especially the method printLogErrorMessages in the DataHandler
benefits from this index.

Resolves: #79696
Releases: master

Change-Id: I3e115b8b5a3cc9cd134d0cc995a06488134be40d
Reviewed-on: https://review.typo3.org/51595


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>