[TASK] Read manifest for class alias files

To be more consistent with composer mode, allow
definition of alias maps in non composer mode as well.

Read the composer manifest for that
(which can be composer.json or ext_emconf.php)

Resolves: #70437
Releases: master
Change-Id: I2f888d7f95dbadc4da1785572fc793a084cf0991
Reviewed-on: http://review.typo3.org/43863


Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Helmut Hummel <helmut.hummel@typo3.org>
Tested-by: Helmut Hummel <helmut.hummel@typo3.org>
Reviewed-by: Nicole Cordes <typo3@cordes.co>
Tested-by: Nicole Cordes <typo3@cordes.co>