[BUGFIX] Doctrine: Consider MySQL index subpart information in upgrade wizards

If an index is defined on a table that is stored on a MySQL database
and uses the MySQL specific subpart length feature add the information
to the schema diff so that the upgrade wizards don't show false
positive changes.

Change-Id: I49eb73c18f7b86aad70d11f3e222c44bd1bd827f
Resolves: #78024
Resolves: #79065
Releases: master
Reviewed-on: https://review.typo3.org/50081


Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: TYPO3com <no-reply@typo3.com>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>