Add background protection when work biometrics is shown

* Remove existing coloured background.
* Add a background with a layout that includes a
  badged icon of the app being opened.

Manual testing steps:
* Set up device with a work profile using TestDPC
* Set a fingerprint in the work profile
* Open a work app
* Lock the device
* Verify the background protection is shown behind
  the biometric prompt

Screenshots:
* Dark mode: https://screenshot.googleplex.com/3SwGWrBREYoZFaH
* Light mode: https://screenshot.googleplex.com/8bzX9wLoFGJ2ado

Bug: 206761107
Test: Manual testing
    WorkLockActivityControllerTest
    TaskStackListenerImplTest
Change-Id: I90d117a97d7457a3186953c16db8bd0bbac048ed