AD Cleanup: Fix confusing naming conventions for synthesized methods and types

[saipraveenb25]

Synthesized methods and types are assigned names in different places and are somewhat inconsistent with their intent.

For instance, the primal context generation function also starts with s_bwd, which can be particularly confusing since it does not compute any derivatives. Probably a good idea to change this to s_primal_ctx or something similar, and have a single point where name synthesis is handled

Additionally, s_diff_ is appended to all processed types even if the type is used as its own differential. This causes existing type names to be overwritten or certain types to have long chains of s_diff_s_diff_... appended to their names. We should clean this up.