Render preview layout in full widgets sheet and bottom widgets sheet

Video: https://drive.google.com/file/d/1gRE0axaq6tm3R_gjSon0RR5lC8HCmwee/view?usp=sharing

Test: Install a sample app which provides a preview layout.
      Go to full widgets sheet to observe widget previews are correctly
      displayed for bitmap previews, layout previews and placeholder
      previews. Repeat the same for bottom widgets picker.
      Pin a widget from a sample app which provide a custom RemoteViews
      preview, observe the custom RemoteViews is correctly rendered.

Bug: 179797520
Change-Id: I2ccd1f77b54a2430d842ee25349fa6e54b9159dc