Implements basic version of Backlinks

- Updated existing and backlinks logic to perform screenshot of and
  query tasks on display that is showing the app clips flow.
- Backlinks changes are guarded behind trunk stable flag.

Bug: 300307759
Test: atest AppClipsActivityTest AppClipsViewModelTest
Flag: com.android.systemui.app_clips_backlinks
Change-Id: I2105164fc6a0af051f545c047a64f1b2f3481bed