Render user's actual workspace in ThemePicker preview (Part 1)

This change takes care of icon rendering. Further work still needs to be done for folders and widgets.

Test: Go to grid options, choose a different grid option, and see user's workspace rendered in the preview
Bug: 144052839
Change-Id: I696153dec1d1f08c5ac82d0c75be5740325c0fc4
5 files changed