Move function schema parser to ATen/core build target (#19282)

Move function schema parser to ATen/core build target (#19282)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/19282

This is largely a hack because we need to use the function schema parser from ATen/core
but aren't clear yet on how the final software architecture should look like.

- Add function schema parser files from jit to ATen/core build target.
- Also move ATen/core build target one directory up to allow this.

We only change the build targets and don't move the files yet because this is likely
not the final build set up and we want to avoid repeated interruptions
for other developers. cc zdevito

Reviewed By: dzhulgakov

Differential Revision: D14931922

fbshipit-source-id: 26462e2e7aec9e0964706138edd3d87a83b964e3