GridPicker get rid of PreviewPager

Also extract the common part of GridFragment and GridFullPreviewFragment into WallpaperPreviewer and GridOptionPreviewer.

Video: https://drive.google.com/file/d/1FkkarDMTfoBzxpDxm04kbb872KyjNpEe/view?usp=sharing

Test: Manually
Bug: 156059583
Change-Id: I0005f4acc3c8b3588d2aca3150b9e17893715871