Create a helper object to wrap polling on multiple file descriptors This helper API can be used to reliably poll on a dynamically increasing set of file descriptors, and it provides a functional callback on top of the C poll() API. As is, it only supports POLLIN as that is what the Sensor API needs, but more event types can be added Bug: 158763319 Test: atest --host android.hardware.sensors@2.0-Google-IIO-Subhal_test-MultiPoll Change-Id: Ifabd1d06b595e93bfaf8e0ffab7b783fbcc73b40