Cleanup to make loading bubble info in background easier

* Moved all the image creation code into BubbleIconFactory & document it
  possibly this is where image caching logic will occur in the future
* BubbleController owns BubbleIconFactory now
* Simplifies some logic in BubbleExpandedView

Test: atest SystemUITests
Bug: 144719337
Change-Id: I91656478e2e542fa943ca00535091ada227ee8ef