Only show split button for single fullscreen task if taskbar is present in...

Only show split button for single fullscreen task if taskbar is present in Overview am: 58433220 am: b8ef284a

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Launcher3/+/20442504



Change-Id: Iadefe00411ce025817f92d8e3a644412cb82a15d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>