`BuilderSystem` for easier system builder construction

[ecoskey]

NOTE: blocked on #21917 or #21916

Objective

• Enable constructing systems from param builders without world access

Solution

• Add BuilderSystem, a wrapper which defers state construction until the first run
• in addition to (...params).build_state(&mut world).build_system(|| {}), now you can also call (...params).build_system(|| {}) directly

Testing

• compiles

(will add more tests while fixing review nits)