Clean up naming and comments (#56964)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56964
This PR does many things but does not update any logic:
- Prefixes all function names that are not `gradcheck`, `gradgradcheck`, `get_numerical_jacobian`, and `get_analytical_jacobian` with underscore to indicate that they aren't part of the public API (https://github.com/pytorch/pytorch/issues/55714).
- Improve naming to avoid referencing Jacobian rows or Jacobian cols when we really mean vjp and jvp as suggested by zou3519
- Try to reduce comment line length so they are more consistent and easier to read
- Other misc improvements to documentaiton
Test Plan: Imported from OSS
Reviewed By: albanD
Differential Revision: D28096571
Pulled By: soulitzer
fbshipit-source-id: d372b5f8ee080669e525a987402ded72810baa0c
