Add Voice activation apps into Settings->Apps->Special app access

This change is flag controlled by
`com.android.settings.flags.enable_voice_activation_apps_in_settings`.

Bug: 306447565
Bug: 303727896
Test: atest com.android.settings.spa.app.specialaccess.VoiceActivationAppsTest
Test: atest com.android.settings.spa.app.specialaccess.VoiceActivationAppsPreferenceControllerTest
Test: manual Settings CUJs
Change-Id: I71a0dc2303263c9957220b56e4dcacec9a561b02