Add video to each gesture preference screen.

- Refactor GesturePreference to a generic VideoPreference.
- The old video_preference.xml is only for magnification video, so
  renamed.
- And use VideoPreference in gesture setting pages.
- Refactor common logic into GesturePreferenceController.

Bug: 32637613
Test: RunSettingsRoboTests

Change-Id: I58580b01a32873cb32c5dc5bf2ec021d5b1400cc