Use Context#createConfigurationContext().

Nothing is changed in the test expectations.
Major changes in this CL are:

  1. To obtain a custom context with the given locale,
     Context#createConfigurationContext() is the way to go.
     Modifying any internal state of the resource that is owned by the
     context is not supported at all.
  2. As a preparation to test cases where multiple locales are specified
     in the system settings, unit tests need to switch to
     Confituration#setLocales(LocaleList).

Bug: 27076327
Change-Id: I6caa76627677c7625a1c42d76a275f67ae65a9b2