Minor change for CaptionAppearanceFragment

1. Move unnecessary public variables into local variables
2. Use %s to update locale preference summary
3. Correct the test case name of CaptionPreviewPreferenceControllerTest

Bug: 197695932
Test: make RunSettingsRoboTests ROBOTEST_FILTER=com.android.settings.accessibility
Change-Id: I58d4d590b9b6d46c27d389217f846a780d755891
10 files changed