Unregister all AOA devices automatically on exit

Pushing a close event from the keyboard_aoa or mouse_aoa implementation
was racy, because the AOA thread might be stopped before these events
were processed.

Instead, keep the list of open AOA devices to close them automatically
from the AOA thread before exiting.

PR #5270 <https://github.com/Genymobile/scrcpy/pull/5270>