Refactor CaptionAppearanceFragment to improve maintainability (1/n)

Root cause: There is a bunch of different logic of preferences in CaptionAppearanceFragment. It’s hard to implement new features and hard to maintain and hard to be testable.
Solution: Move out preview preference logic of CaptionAppearanceFragment into controllers to reduce the complexity of the relationship between preference and fragment.

Bug: 197695932
Test: make RunSettingsRoboTests ROBOTEST_FILTER=com.android.settings.accessibility
Change-Id: Ie8acdcb8659606ce3faf6d5532cc73ee19024725