Implement firing of Startup/Shutdown events as defined by CDI 4

As part of https://github.com/eclipse-ee4j/cdi/issues/496, CDI introduced Startup and Shutdown events to indicate container state.
These are standard CDI events observable from any bean.

Weld is currently lacking implementation (and CDI is lacking a TCK test) as well as tests.
We should be firing these events at the same time as we fire @Initialized(ApplicationScoped.class) and its respective counterpart.

Note that since Weld can run in SE, servlet and EE, we might need to implement this in several places.