Implement common ImageLoader in SystemUI

The image loader will allow size restricting loaded images and also
default to loading bitmaps in Config#HARDWARE configuration. It's meant
to unify how we do image loading across SysUI.

Bug: 274881334
Change-Id: I00732e2ca97b260d1984a14925a78ff78349a6c6
Test: Newly created unit tests for the code