[mlir][python] add `owner` to OpResultsList.

[makslevental]

Summary

this is useful for when the list is empty and an element can't be used to fetch the owner.

mlir/lib/Bindings/Python/IRCore.cpp

PyOpResultList(PyOperationRef operation, intptr_t startIndex = 0,
                                : length,
                   step),
         operation(operation) {}
 
   static void bindDerived(ClassTy &c) {
     c.def_property_readonly("types", [](PyOpResultList &self) {
       return getValueTypes(self, self.operation->getContext());
     });
+    c.def_property_readonly("owner", [](PyOpResultList &self) {
+      return self.operation->createOpView();
+    });
   }
 
 private:
   /// Give the parent CRTP class access to hook implementations below.
   friend class Sliceable<PyOpResultList, PyOpResult>;
 
   intptr_t getRawNumElements() {
     operation->checkValid();

mlir/test/python/ir/operation.py

 # CHECK-LABEL: TEST: testOperationResultList
 @run
 def testOperationResultList():
     ctx = Context()
     module = Module.parse(
         r"""
     func.func @f1() {
       %0:3 = call @f2() : () -> (i32, f64, index)
+      call @f3() : () -> ()
       return
     }
     func.func private @f2() -> (i32, f64, index)
+    func.func private @f3() -> ()
   """,
         ctx,
     )
     caller = module.body.operations[0]
     call = caller.regions[0].blocks[0].operations[0]
     assert len(call.results) == 3
     # CHECK: Result 0, type i32
     # CHECK: Result 1, type f64
     # CHECK: Result 2, type index
     for res in call.results:
         print(f"Result {res.result_number}, type {res.type}")
 
     # CHECK: Result type i32
     # CHECK: Result type f64
     # CHECK: Result type index
     for t in call.results.types:
         print(f"Result type {t}")
 
     # Out of range
     expect_index_error(lambda: call.results[3])
     expect_index_error(lambda: call.results[-4])
 
+    no_results_call = caller.regions[0].blocks[0].operations[1]
+    assert len(no_results_call.results) == 0
+    assert no_results_call.results.owner == no_results_call
+
 
 # CHECK-LABEL: TEST: testOperationResultListSlice
 @run
 def testOperationResultListSlice():
     with Context() as ctx:
         ctx.allow_unregistered_dialects = True
         module = Module.parse(
             r"""