Reflection Service should ignore leading backslashes in class names
While reflecting classes it could happen that the reflection service caches for example class names of interface implementations with or without a leading backslash, depending on how the class was specified in some annotation. This is error prone and therefore the reflectClass method should silently trim a leading backslash.
While at it, the Object Manager could give some hint in its API methods that an object could probably only not be found because a leading backslash was given - which is not allowed.
[+TASK] FLOW3 (Object): The Abstract Object Container now gives a hint / throws an InvalidArgumentException if object names or class names were specified with a leading backslash. Relates to #7198
[+BUGFIX] FLOW3 (Reflection): The Reflection Service now ignores leading backslashes in class names specified in annotations. Resolves #7198
[+BUGFIX] FLOW3 (Persistence): The Persistence Manager now retrieves repository objects by object name instead of class name. Resolves #7199