injects into returned instance when mapped with toType

[g10]

The objects retrieved with getInstance() are themselves getting injected on creation (for the objects that are mapped on the injector with toType).

[g10]

2nd commit also adds this behaviour for toSingleton() + only initialize the singleton when it is requested with getInstance()

The late initialization is useful if an app has a config fase (where the mapping on the injector is done) before actual initialization of the app, the mappings can be done regardless of the presence of a dependent injection, as long it is present at the time (eg. app initialization fase) the (singleton) class is requested from the injector.