Make sure the secondary TaskFragment is above the primary Before, we may reuse the existing TaskFragment for secondary activity, which may be below the primary TaskFragment. Now, we make sure the secondary TaskFragment is always on top. Bug: 244254584 Test: atest WMJetpackUnitTests:SplitPresenterTest Test: atest WMJetpackUnitTests:TaskFragmentContainerTest Change-Id: Id4c240af71fbd344126ae8bbbad57d9c2150d550