Add postured dream setting

This adds a new entry into the dream settings for 'While stationary and upright'. When this is enabled, dreams will be activated when the device is stationary and upright.

Bug: 383208131
Test: locally - mp droid and verified entry shows up in settings UI and
writes to Settings.Secure correctly
Flag: android.service.dreams.allow_dream_when_postured

Change-Id: Id38d5a6fc121be36a16d4bdfc6c40fcc59e3c085