Add settings and reset operations for demo users

- Allow Global settings to be set in demo mode
- Allow Secure settings to be set by demo users
- Allow fully enabling apps for demo users
- Send enable broadcast as foreground broadcast

Bug: 62712426
Test: runtest -c \
com.android.server.devicepolicy.DevicePolicyManagerTest \
frameworks-services

Change-Id: Icd5d1eda12aa6b97bd4770713710a982bb0fc8e5