Allow TestLooperManager access from current thread.

TestLooperManager would previously deadlock if both
acquire and next were called from the Looper's current thread.

This commit changes TestLooperManager to detect if acquire
and next was called from Looper's thread.

See: go/testable-messagequeue-bluedoc

Bug: 379472827
Flag: android.os.message_queue_testability
Test: android.os.cts.TestLooperManagerTest
Change-Id: Id458145cdac5d4e507e1d4d2c809b9d8a66a6ac2