Launch `UserSwitchDialog` using the expandable

The old `UserSwitchDialogController` class would utilize the
`Expandable`, and had the dialog launch itself by creating a
`DialogLaunchAnimator.Controller` from the expandable.

This CL threads the expandable through to the
UserSwitchDialogCoordinator so it can do something similar.

Test: UserInteractorTest; manual
Bug: 260874319
Change-Id: I86e7df6b8aaa1dccc0cb951c491fd8c6b30294e1
Merged-In: I86e7df6b8aaa1dccc0cb951c491fd8c6b30294e1