New feature “Text and reading options” for SetupWizard, Wallpaper, and Settings (12/n).

- Link-up between the preview, font size, and display size preferences.
- Add the preview preference and entry.

Bug: 211503117
Test: make RunSettingsRoboTests ROBOTEST_FILTER=TextReadingPreviewControllerTest
Test: make RunSettingsRoboTests ROBOTEST_FILTER=TextReadingPreviewPreferenceTest
Change-Id: Ic6c48861a0051670fd78b13dca5488711de30cb8