Add missing Theme.DeviceDefault.Dialog on TV

To ensure that we have TV themed dialogs we should add this. It is being
used by Theme.DeviceDefault.System.Dialog as well as other SystemUI
themes.

Bug: 264981854
Test: manual - start a screen recording and check that the dialog looks
good and TV themed

Change-Id: I275ffaf2df5c394a2a12e547f0c0c249d88d0d36