[FEATURE] Add check if local extensions can be loaded

Add a check in the install tool that checks if all local
extensions can be loaded without fatal errors by including
ext_localconf and ext_tables files.

Change-Id: I30ff00af83e59681c52901ecc09889f5c3cd4243
Releases: 6.2
Resolves: #49760
Reviewed-on: https://review.typo3.org/22047
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters