[TASK] Add missing index on table sys_file_reference

During copying of pagetrees various sql statments
are executed. One on sys_file_reference has a bad
performance and can benefit from an index.

Fixes: #79604
Releases: master

Change-Id: I2caa83db6259ad6baad75427b5040a11ece768ba
Reviewed-on: https://review.typo3.org/51512


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Joerg Boesche <typo3@joergboesche.de>
Tested-by: Joerg Boesche <typo3@joergboesche.de>
Reviewed-by: Stephan Großberndt <stephan@grossberndt.de>
Reviewed-by: Christer V <cvi@systime.dk>
Reviewed-by: Claus Due <claus@phpmind.net>
Tested-by: Claus Due <claus@phpmind.net>
Reviewed-by: Morten Pless <mpl@systime.dk>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>