For internal libraries (as opposed to the client libraries), we currently use a mix of the 'Library' and 'StaticLibrary' rules. By default, 'Library' means the same thing as 'StaticLibrary', so there is no difference.

We should standardize and change all current calls to 'StaticLibrary' to 'Library', and reserve 'StaticLibrary' and 'SharedLibrary' for the explicit case where we wish to produce a library of particular type.

This will also make it easier if, in the future, we ever want to inject particular behavior into our internal libraries, as we will only need to override the 'Library' target, but can leave 'StaticLibrary' and 'SharedLibrary' alone.