Use FragmentActivity instead of AppCompatActivity

Use FragmentActivity instead of AppCompatActivity
since AppCompatActivity doesn't support platform
level dramatic color change.

Bug: 216638097
Test: atest CtsCompanionDeviceManagerCoreTestCases
      atest CtsCompanionDeviceManagerUiAutomationTestCases
      atest CtsOsTestCases:CompanionDeviceManagerTest
Change-Id: I6d52bf37fa72c4266d1d1941325b6a63a8ab2643
4 files changed