Merge pull request #18577 from etiennesegonzac/bug-999478-on-demand-callscreen

Bug 999478 - Free the preloaded callscreen under memory pressure
(cherry picked from commit 03da6aab8a033d83835a245c968ce4dd2f06409e)

Conflicts:
	apps/system/js/attention_screen.js
	apps/system/js/dialer_agent.js