Fixed SaveUi on Autofill for visible background users.

It needs to set the proper display in the FillUI context, otherwise
it's rendered in the wrong display.

Test: atest --user-type secondary_user_on_secondary_display CtsAutoFillServiceTestCases:android.autofillservice.cts.dropdown.LoginActivityTest#testAutoFillOneDatasetAndSave
Test: atest CtsAutoFillServiceTestCases # on phone
Bug: 271031908

Change-Id: I4f5700c75bbca0afb2008e51146a01b4e3d70f5b