Convert some of the calls to *Factory.getPrimitive(keyset) to keyset.getPrimitive<*>() in our codebase.

The goal is to get the documentation up to date, but we just start with a chunk.

PiperOrigin-RevId: 219786142
GitOrigin-RevId: 7c6f3ead37fe00ac641b1a8f849d9ac738980b4a