Handle duplicate backlinks in app clips

- When multiple backlinks with same app name are available, the names
  are suffixed with numerical index for identification.

Bug: 356791827
Flag: com.android.systemui.app_clips_backlinks
Test: atest AppClipsActivityTest AppClipsTest
Change-Id: I24a9c841f78efda5d221ef8798ca63c5b7f9cde5