[TASK] Add index to slug field

`TYPO3\CMS\Core\Routing\PageRouter::getPagesFromDatabaseForCandidates`
looks-up candidates for the page using the `slug` field (and also sorts by
this value). This has some serious impact on the website performance on
systems with lots of pages. In order to optimize this, an index should be
set.

Releases: master
Resolves: #88896
Change-Id: I1aecca781db9562243a15341819b3ce261708836
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/61403


Tested-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Jonas Eberle <flightvision@googlemail.com>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Jonas Eberle <flightvision@googlemail.com>
Reviewed-by: Benni Mack <benni@typo3.org>

typo3/sysext/core/ext_tables.sql

@@ -115,7 +115,8 @@ CREATE TABLE pages (
 	legacy_overlay_uid int(11) unsigned DEFAULT '0' NOT NULL,
 
 	KEY determineSiteRoot (is_siteroot),
-	KEY language_identifier (l10n_parent,sys_language_uid)
+	KEY language_identifier (l10n_parent,sys_language_uid),
+	KEY slug (slug(127))
 );
 
 #