Update the strings on app unavailable alert dialog

- Update strings on Settings unavailable alert dialog to match
  UX guidelines.
- Update strings on other apps unavailable alert dialog to
  match UX guidelines.
- Add the test cases.

Bug: 227283466
Test: Manual, atest FrameworksServicesTests:VirtualDeviceManagerServiceTest
Change-Id: I9a527db49e3f6e6d3c147a18a3e4c8e403cda6bd