Add missing cubeb_stream_get_latency wrapper.

From 1b8702d0003f93b24974432ab667bee2ed4b041f.
audiotrack: Look up getOutputSamplingRate for all versions of Android.
audiotrack: round up minimum latency value.  (bug 930189)
wasapi: Remove hardcoded 30ms latency limit.  (Bug 933198)
wasapi: Support mono output configurations.  (Bug 929009)