Launch the platform easter egg in a new task.

This ensures that when PlatLogoActivity is launched on a
large-screen device, it properly takes over the full screen
(and doesn't hide the status bar for Settings!).

Bug: 243407943
Test: make RunSettingsRoboTests ROBOTEST_FILTER=FirmwareVersionDetailPreferenceControllerTest
Change-Id: Icf10aa43e5b4a27a2fa98ea41b5a9e9cf659e895