Do not look for in-process activities if contains other process activities

The #findActivityBelow looks for the in-process activities first to
get the activity behind the given activity. However, it may not be
correct if the container contains activities of another process.

Bug: 271769839
Test: SplitControllerTest
Change-Id: I8794c55a56712113dc318aa4a0f440c90589378d
3 files changed