Add convenient method to get generic beans by type reference

[quaff]

Feel free to close if the team think it's not worthy.

[jhoeller]

Actually, I'd like to avoid such further overloads there. If at all, we'd introduce a getBeanProvider(ParameterizedTypeReference) method (since there is no getBean(ResolvableType) method either, just getBeanProvider(ResolvableType)), and such an ObjectProvider-returning method would then just have the ResolvableType.forType convenience without further value.

Thanks for the PR, in any case!