Fix testable looper threading

In the case where an annotation was not used and the TestableLooper
was manually created, then the messages would be executed on the wrong
thread.

Also switch some handlers over to async, might save us a little time.

Test: runtest --path frameworks/base/tests/testables
Bug: 79550837
Change-Id: I70a36449ae08eb5799e2dad41a5d258bb51a3fd3