Fix DMSTests

DisplayManagerServiceTests were failing with error:
"You cannot keep your settings in the secure settings."

- testPhysicalViewports
- testCreateVirtualDisplay_sentToInputManager

This was occurring since we dont have permission to write to these
settings during the test. To improve and fix the tests we'd prefer to use a fake settings provider.

Bug: 275079012
Test: atest DisplayManagerServiceTest
Change-Id: Ia7a07081070ca88fd5e05b1c7463941f47374682