[mlir][python] Forward _OperationBase _CAPIPtr to the Operation.

[stellaraccident]

Summary

• ODS generated operations extend _OperationBase and without this, cannot be marshalled to CAPI functions.
• No test case updates: this kind of interop is quite hard to verify with in-tree tests.

mlir/lib/Bindings/Python/IRCore.cpp

py::class_<PyModule>(m, "Module", py::module_local())
             return printAccum.join();
           },
           kOperationStrDunderDocstring);
 
   //----------------------------------------------------------------------------
   // Mapping of Operation.
   //----------------------------------------------------------------------------
   py::class_<PyOperationBase>(m, "_OperationBase", py::module_local())
+      .def_property_readonly(MLIR_PYTHON_CAPI_PTR_ATTR,
+                             [](PyOperationBase &self) {
+                               return self.getOperation().getCapsule();
+                             })
       .def("__eq__",
            [](PyOperationBase &self, PyOperationBase &other) {
              return &self.getOperation() == &other.getOperation();
            })
       .def("__eq__",
            [](PyOperationBase &self, py::object other) { return false; })
       .def_property_readonly("attributes",
                              [](PyOperationBase &self) {