Support secondary_user_on_secondary_display in CtsAppWidgetTestCases

secondary_user_on_secondary_display is for background users that have
access to UI on assigned displays (a.k.a. visible background users) on devices that have config_multiuserVisibleBackgroundUsers enabled. The main use case is Automotive's multi-display Whole Cabin experience where
passengers (modeled as visible background users) can interact with the display in front of them concurrently with the driver (modeled as the the current user) interacting with driver's display.

- Add secondary_user_on_secondary_display option.

Bug: 348864476
Test: atest CtsAppWidgetTestCases
Test: atest --user-type secondary_user_on_secondary_display CtsAppWidgetTestCases
(cherry picked from https://partner-android-review.googlesource.com/q/commit:bff8fd74a907502a3806f29a4fe58e9b9013985b)
Merged-In: Ie182eafd54733abfc58ad02b8035bc7d8bd92227
Change-Id: Ie182eafd54733abfc58ad02b8035bc7d8bd92227