Select remote apps based on stagePosition instead of hardcoded values

* LauncherSplitScreenListener returns taskIds guaranteeing index 0
to be leftTop task and index 1 to be rightBottom. Use that
instead of assuming remote target index 0 will be leftTop and
index 1 is right bottom as provided

Bug: 181704764

Change-Id: I2bc358ff3c2f2d127b81e10824e2c13f3ad718df
2 files changed