Merge "Center drop target icons in landscape mode." into sc-dev am: 3287dd9fa7 am: 62d2706244 am: 441ee2494a

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Launcher3/+/14980961

Change-Id: I0c14a7cb008adfaa3745d01e4536d1c82dbbb1eb