Reland "Do not add display area features for untrusted display"

Untrusted display (e.g. virtual display created by app, a common
case is screen recorder) doesn't support system decorations. There
is nothing to do with additional features.

This saves 31 areas (according to current features) per untrusted
display. And also reduce the cost of traversing entire hierarchy.

Reland since making DisplayContent#getWindowingLayer() valid by
commit 941ad3a5.

Fixes: 175179353
Test: DisplayAreaPolicyTests#testEmptyFeaturesOnUntrustedDisplay
Test: Start Desktop Head Unit (simulation of Auto)
Change-Id: I3929d17eab6bed3f1358d6782e363120f0edd385