FRP ConfirmDeviceCredentialActivity launched in initial setup flow should belong to internal flow, so it needs to set the external flag to false. It can transmit setup intent extra to the stencil library to make the screen be applied to the stencil and BC layout.
Bug: 171950236
Test: Manual test & RunSettingsGoogleRoboTests
Change-Id: Ia98d1bb4fc3a1687992b202b1e58afc1463efaf4