Fix Linux UI issues introduced by moving llinitparam to llcommon.

In a number of places, the viewer uses a lookup based on std::type_info*. We
used to use std::map<std::type_info*, whatever>. But on Linux,
&typeid(SomeType) can produce different pointer values, depending on the
dynamic load module in which the code is executed. Introduce
LLTypeInfoLookup<T>, with an API that deliberately mimics
std::map<std::type_info*, T>. LLTypeInfoLookup::find() first tries an
efficient search for the specified std::type_info*. But if that fails, it
scans the underlying container for a match on the std::type_info::name()
string. If found, it caches the new std::type_info* to optimize subsequent
lookups with the same pointer.
Use LLTypeInfoLookup instead of std::map<std::type_info*, ...> in
llinitparam.h and llregistry.h.
Introduce LLSortedVector<KEY, VALUE>, a std::vector<std::pair<KEY, VALUE>>
maintained in sorted order with binary-search lookup. It presents a subset of
the std::map<KEY, VALUE> API.