R1:52112620a3d2

Provide a pure APC cache for runtime caching

Summary:
Ref T11954. Depends on D16992. We have some data which can be generated and cached at runtime. Three examples are:

- Class map from Conduit method names to implementing classes.
- Class map from PHID types to implementing classes.
- The main routing map.

None of these are huge wins but they impose global costs and can be shaved down through caching without introducing an enormous amount of new complexity.

The cost to these maps is that…