Revert "Do not show Home behind full screen activity"

This reverts commit 1eb3e4549d77a4d2eee57df1226d8a8184d2b7f9.
Revert "[ActivityManager] Ensure consistency behavior when a background activity brings another existed activity to front."

This reverts commit 1e756746441c6105c65f9935ddeaaaed26359680.
Revert "[ActivityManager] Fix a bug: unable to start activity after starting activities during screen off."

This reverts commit 626e6ab304e22a2f86039c3a245801d4ae1576cd.