MAINT-1175: Ditch LLTypeInfoLookup, make map<const type_info*> work.

Instead of forbidding std::map<const std::type_info*, ...> outright (which
includes LLRegistry<const std::type_info*, ...> and LLRegistrySingleton<const
std::type_info*, ...>), try to make it work by specializing std::less<const
std::type_info*> to use std::type_info::before().
Make LLRegistryDefaultComparator<T> use std::less<T> so it can capitalize on
that specialization.