Add icon to desktop tile in overview

Copied over icon from caption desktop button in WMShell. Temporary icon
for now.
Refactored some logic in TaskView to better support for custom
orientation handling in subclasses. Subclasses can override setting
orientation for icon or thumbnail.

Bug: 267326722
Test: manual, enable desktop windowing proto 2 and go to overview
Change-Id: Id66d48fa52a418a07b954a384b2c3ea22f091b1f