User Switcher: Polish tap on user switcher.

Make user switcher immediately tappable when launched from the
lockscreen. There is a noticeable lag when tapping the buttons when
launchign from the lockscreen. This is because of occlusion animations
done with startActivity. Additionally, report tap in the status bar to
remove tap penalty. This will lighten the restriction of the falsing
amanger on the user switcher.

Also added a test file.

Bug: 223558461
Test: Manual on device
Change-Id: I010164a6fc968a22324164356aa93bea21eab41c