Open user switcher with status bar context when opened from chip

The user switcher dialog was being opened always with the shade context:
 it means it was always a subwindow of the shade window, and visible
 only when the shade was visible (after the changes introduced by
 I43b6d34ba24d338ea08ab67893a0e121cddcceb2)

Now, the ShowDialogRequestModel also supports a custom context. When
provided, the dialog is created with such context (e.g. when touching a
status bar user chip, the dialog will now appear on that display,
regardless of the shade window position.

Bug: 362719719
Bug: 414780857
Test: UserSwitcherInteractorTest
Flag: com.android.window.flags.enable_window_context_override_type
Flag: com.android.systemui.shade_window_goes_around
Change-Id: I6abd72194bfeb0b8915821f055cedd816822c8c4