TestLooperManagerTest add debugging

In doTest, dump the current message if we are about to fail an assert.

Dump timestamps in peekWhen_future.

Also call tlm.poll() instead of tlm.next(). If we stop seeing failures
in doTest() then that might indicate some issue with next().

Test: atest TestLooperManagerTest
Bug: 385010271
Flag: android.os.message_queue_testability
Change-Id: Ic809550ce2727c5aa27ccecdf6a79b2627dbcb26