Consider the lock-task mode while using FLAG_ACTIVITY_TASK_ON_HOME

The flag will cause a newly launching task to be placed on top of the
current home activity task but it did ignore the lock-task mode
mechansim.

This CL checks the home task whether violated with lock-task mode when
startActivity with task-on-home flag.

Bug: 202980858
Test: atest TaskTests#testReturnsToHomeRootTask
      atest ActivityVisibilityTests#testLaunchTaskOnHome
Change-Id: I521b9e4fc32648263afb70de3342dbb5f3583330