Replace display orientation in PinnedStackTests

The test assumes that, since the windowing mode of the activity is fullscreen, setting it's orientation to landscape will result in updating the device orientation to landscape as well. This does not happen on Duo because of our task organization in display areas that ignore orientation requests.

Solution: Since the plan seems to be to support display area orientation without affecting the orientation of the device and since the scope of this specific test is to validate that the orientation of the activity is updated, not the one of the device, the solution we propose is to assert that the orientation of the activity task is set to landscape.

Bug: 190630852
Test: run command cts -m CtsWindowManagerDeviceTestCases -t android.server.wm.PinnedStackTests#testSetRequestedOrientationWhilePinned
Verified on: Pixel 4 XL & development device

Change-Id: I2e8e169edbcb899d85ba4d98f4f5a818698ccb5c