Fix test failures in UserManagerStateTest and FileCopyUiTest.

Using mocked context.Resources instead of Instrumentation's target
context resolves the failures in version R and S. Ignoring tests in
FileCopyUiTest as it is flaky in local run istelf.

Bug: 327894939
Test: atest DocumentsUIGoogleTests:UserManagerStateTest
Change-Id: I57fa84dcfd05241468534ad59de40cda5f3ec371