Turn on the "use standby to exit vr mode" feature

Set "use standby to exit vr mode" to true by default. This keeps
standalone devices in vr mode for a period of time after the user doffs
the headset.

Bug: 65248224

Test: I set the flag to true on a standalone. I went through OOBE, used
VrHome and other apps, doffing/donning at each step and ensuring the
device stays in vr mode and resumes normal operation after donning.

Change-Id: I4ae54606b2af49b8aaff2388d88d6b505bd01395