Add support for shared scenes that have client + server components in them
- avoids adding complexity of running preprocess at build time to first release
- handles editor only spawning a single monument
- keep support for client only & server only scenes
- default to only building shared scenes rather than individual client & server scenes
- run preprocess at runtime for shared scenes instead of during build
- internally refered to as "generic" scenes because "shared" is easy to mix up with "server"