Merge "Add API to query number of visible desktop tasks" into tm-qpr-dev am: 0927efa873 am: 7c9c5b7d7b

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/20969963

Change-Id: I80e66d8532c96853275acdf824416e5db805a15e
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>