Issue Description:

It is possible to import std::vector using our general strategy to import templates (import only full specializations), however, for a vocabulary type like std::vector that might be too limiting, as the imported type won't be usable with type variables.

One idea is to reimplement std::vector in Swift: implement a generic Swift struct with identical memory layout to std::vector.

Fortunately, in libc\\, sizeof(std::vector<int>) == sizeof(std::vector<bool>), so all specializations have identical size. In libstdc++ that is not the case.

I'm not sure this idea will work out well, but it is worth trying.