[mlir][Pass] Add a tablegen backend for defining Pass information

This will greatly simplify a number of things related to passes:
* Enables generation of pass registration
* Enables generation of boiler plate pass utilities
* Enables generation of pass documentation

This revision focuses on adding the basic structure and adds support for generating the registration for passes in the Transforms/ directory. Future revisions will add more support and move more passes over.

Differential Revision: https://reviews.llvm.org/D76656