Add infrastructure to provide/identify managed types.

[christophstrobl]

The MappingContext allows to define a set of initial entities used to compute metadata early instead of first encounter. Those types are identified in multiple ways, depending if set by the user, boot or data itself. The latter two make use of the identifying annotations provided by the store module implementation.
Being buried within the mapping context, potential AOT processing is hardly possible.

Desired State:

• Each store registers a bean holding references to the type names it needs to know about if not provided externally
• Mapping context obtains the bean and uses the given types to initialize the mapping context.
• Public infrastructure that does the entity scanning so we do not have different implementations in data and boot.