DRTVWR-564: Allow LLLeapListener to report LazyEventAPIs too.

One important factor in the design of LazyEventAPI was the desire to allow
LLLeapListener to query metadata for an LLEventAPI even if it hasn't yet been
instantiated by LazyEventAPI. That's why LazyEventAPI requires the same
metadata required by a classic LLEventAPI.

Instead of just publicly exposing its data members, give LazyEventAPI a query
API mimicking LLEventAPI / LLEventDispatcher. Protect data members and private
methods.

Adapt lazyeventapi_test.cpp accordingly.

Extend LLLeapListener::getAPIs() and getAPI() to look through LazyEventAPIBase
instances after first checking existing LLEventAPI instances. Because the
query API for LazyEventAPIBase mimics LLEventAPI's, extract getAPI()'s actual
metadata reporting to a new internal template function reportAPI().

While we're touching LLLeapListener, we no longer need BOOST_FOREACH().