Create sysprop to disable connected display dialog.

Add a system property to enable an external display on connection
instead of disabling it. This will cause the UI dialog to not show up
when an external display is connected.

Test: Manual
Test: atest DisplayManagerServiceTest
Bug: 306178462
Change-Id: I06187462287566a9f4e5a1296b511577014d843f
2 files changed