[BUGFIX] Add TCA migration for columnsOverrides as well

When migrating old TCA configuration to overrideChildTca,
we must respect columnsOverrides and do the migration there as well.

Also fix the examples for overriding cropVariants, which missed some
nesting levels

Resolves: #80493
Releases: master
Change-Id: If38f445e545b6f93eead5f30cfc16e787343b8c6
Reviewed-on: https://review.typo3.org/52189


Reviewed-by: Frans Saris <franssaris@gmail.com>
Tested-by: Frans Saris <franssaris@gmail.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>