Support FLAG_ACTIVITY_LAUNCH_ADJACENT for launch root with adjacent

Add window container transaction APIs to indicate launch root for task
launching with FLAG_ACTIVITY_LAUNCH_ADJACENT. If launch adjacent flag
root is available, consider to launch to its adjacent task if the launch
is coming from the same root task.

Fix: 169271875
Test: atest WMShellUnitTests
Test: atest TaskDisplayAreaTests
Test: manual test FLAG_ACTIVITY_LAUNCH_ADJACENT behavior with adjacent
root.

Change-Id: I1716aaa48745d2c32cd413c8eac0b1d17810f0de