Get flaky test out of pre-submit and move non-flaky test into it.

The two tests in TaskStackChangedListenerTest is no longer flaky and the
flaky annotation was removed before. But the presubmit annotation is
missing. Promote them into presubmit.

The test testProcessTwoItems_OneAfterAnother caused 29 flakes during the
past 7 days. Move it out of pre-submit first.

Bug: 123654474
Bug: 128526085
Test: atest PersisterQueueTests
Test: atest TaskStackChangedListenerTest
Change-Id: Iffe89b6b441cd1ecb67e7d77220dd5d282cd57cd