[mlir][linalg] Add structured op builders from python opdsl.

* Makes the wrapped functions of the `@linalg_structured_op` decorator callable such that they emit IR imperatively when invoked.
* There are numerous TODOs that I will keep working through to achieve generality.
* Will true up exception handling tests as the feature progresses (for things that are actually errors once everything is implemented).
* Includes the addition of an `isinstance` method on concrete types in the Python API.

Differential Revision: https://reviews.llvm.org/D98754