Provide a step container to OpKernelContexts when running eagerly.

This lets us run some ops that require step containers (e.g.
TensorArray-related ops).

 Before change:
 Benchmark                    Time(ns)        CPU(ns)     Iterations
-------------------------------------------------------------------
 BM_CreateGraph                  61292          80915           8581
 BM_RunGraph                      7899          13398          51251
 BM_CreateAndDestroySession       2588           2594         269838
 BM_KernelAndDeviceInit           2971           2976         235908
 BM_KernelAndDeviceRun             505            506        1000000

 After change:
 Benchmark                    Time(ns)        CPU(ns)     Iterations
 -------------------------------------------------------------------
 BM_CreateGraph                  78295         105539           8698
 BM_RunGraph                      9907          16988          47908
 BM_CreateAndDestroySession       2773           2778         247635
 BM_KernelAndDeviceInit           2678           2682         270054
 BM_KernelAndDeviceRun             553            554        1000000

PiperOrigin-RevId: 198125630