[mlir][python] Aggressively avoid name collisions in generated python ODS code.

* When porting npcomp to use these bindings, I ran into enough patterns of collisions that I decided to be somewhat draconian about not polluting the namespace.
* With these changes all of the npcomp dialects generate and pass what tests we have.

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D93920