Support multiple target dependencies with the same package id but different versions.

Currently target dependencies are specified through a map where the key is the `package:name` package id. However, multiple dependencies can have the same id if they are of different versions. It seems it is currently impossible to satisfy two dependencies if they have the same `package:name` identifier.

I'm not sure the right way to solve this issue. Cargo component models dependencies as a `HashMap` where the keys are `PackageId`s, but there might be more than one dependency with the same package id. It might seem that we would have to rethink how these dependencies are specified.