Use postStartActivityDismissingKeyguard when showOnLockscreen is false.

This fixes the issue where the timer app becomes visible when the
lockscreen isn't fully dismissed. See b/250476316#comment6, step 2.

The relevent code path is the one using intent. But also made the same
change for the pending intent code path.

Bug: 250476316
Test: click on Smartspace timer on lockscreen.

Change-Id: I0ca16b535ff06a80db09640078e9c961fe29a60e