MAINT-1175: Change LLTypeInfoLookup API for future optimizations.

Per discussion with Richard, accept the type key for insert() and find() as a
template parameter rather than as std::type_info*. This permits (e.g.) some
sort of compile-time prehashing for common types, without changing the API.
Eliminate iterators from the API altogether, thus avoiding costs associated
with transform_iterator.
Fix existing references in llinitparam.h.