[BUGFIX] Ensure new extension classes are loaded

If you install any extension during the update, the classes are still
unknown. This is because the static autoload files aren't regenerated
after the installation. This patch triggers the update of class loading
information after an extension was installed.

Resolves: #71507
Releases: master
Change-Id: I6004ef2d7c10608c738037002380ea520bec03b8
Reviewed-on: https://review.typo3.org/44689


Reviewed-by: Helmut Hummel <helmut.hummel@typo3.org>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>