Exclude the embedded tasks from Recents

Currently embedded tasks with activities from other apps are showing
as separate entries in Recents. We should only have a single Recents
entry for the host and embedded apps as per UX definition. This CL
excluded the entry from recents if the task is embedded.

Bug: 194243805
Test: atest RecentTasksTest#testVisibleEmbeddedTask_expectNotVisible
Change-Id: Ie4548ffc0175a1c331f3509fe9ded8c1a1a53196