[MLIR] [Python] Add `owner` to PyValue and fix its parent reference

[jdd]

Summary

Adds owner python call to mlir.ir.Value.

Assuming that PyValue.parentOperation is intended to be the value's owner, this fixes the construction of it from PyOpOperandList.

[stellaraccident]

Thanks - this looks right to me.

mlir/lib/Bindings/Python/IRCore.cpp

PyOpOperandList(PyOperationRef operation, intptr_t startIndex = 0,
         operation(operation) {}
 
   intptr_t getNumElements() {
     operation->checkValid();
     return mlirOperationGetNumOperands(operation->get());
   }
 
   PyValue getElement(intptr_t pos) {
-    return PyValue(operation, mlirOperationGetOperand(operation->get(), pos));
+    MlirValue operand = mlirOperationGetOperand(operation->get(), pos);
+    MlirOperation owner;
+    if (mlirValueIsAOpResult(operand))
+      owner = mlirOpResultGetOwner(operand);
+    else if (mlirValueIsABlockArgument(operand))
+      owner = mlirBlockGetParentOperation(mlirBlockArgumentGetOwner(operand));
+    else
+      assert(false && "Value must be an block arg or op result.");
+    PyOperationRef pyOwner =
+        PyOperation::forOperation(operation->getContext(), owner);
+    return PyValue(pyOwner, operand);
   }
 
   PyOpOperandList slice(intptr_t startIndex, intptr_t length, intptr_t step) {
     return PyOpOperandList(operation, startIndex, length, step);
   }
 
   void dunderSetItem(intptr_t index, PyValue value) {
     index = wrapIndex(index);
py::class_<PyValue>(m, "Value")
       .def(MLIR_PYTHON_CAPI_FACTORY_ATTR, &PyValue::createFromCapsule)
       .def_property_readonly(
           "context",
           [](PyValue &self) { return self.getParentOperation()->getContext(); },
           "Context in which the value lives.")
       .def(
           "dump", [](PyValue &self) { mlirValueDump(self.get()); },
           kDumpDocstring)
+      .def_property_readonly(
+          "owner",
+          [](PyValue &self) {
+            assert(mlirOperationEqual(self.getParentOperation()->get(),
+                                      mlirOpResultGetOwner(self.get())) &&
+                   "expected the owner of the value in Python to match that in "
+                   "the IR");
+            return self.getParentOperation().getObject();
+          })
       .def("__eq__",
            [](PyValue &self, PyValue &other) {
              return self.get().ptr == other.get().ptr;
            })
       .def("__eq__", [](PyValue &self, py::object other) { return false; })
       .def(
           "__str__",
           [](PyValue &self) {