Fix VisibilityPreferenceControllerTest.

The test was expecting an ArgumentCaptor for RestrictedDropDownPreference
(extends ListPreference).setEntryValues(CharSequence[]) to be passed an
array of Strings, when actually it should have expected an array of
CharSequences.

This CL fixes the test to use CharSequence. Since CharSequence.equals()
is not guaranteed to be in terms of value equality of the characters,
a private static helper method:

  List<String> toStringList(CharSequence[] charSequences) { ... }

is used.

Bug: 70504129
Test: EXPERIMENTAL_USE_OPENJDK9=1.8 make -j30 showcommands dist \
  RunSettingsRoboTests RunSettingsRoboTests-jacoco \
  RunSettingsLibRoboTests RunSettingsLibRoboTests-jacoco \
  RunSettingsGoogleRoboTests RunSettingsGoogleRoboTests-jacoco \
  RunSuwRoboTests RunSuwRoboTests-jacoco \
  RunTurboRoboTests \
  RunStorageManagerRoboTests \
  RunTvSettingsRoboTests RunTvSettingsRoboTests-jacoco

Change-Id: I347b03e6cb01715cd1c7f50b5f36567e5f375ad7